I am a newbie, I am angry and let me vent.
Why the heck are there two firewalls on my kde neon installation and that too without informing me? Most probably an oversight.
There is the

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 ufw

and then there is lo-and-behold

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 plasma-firewall

.
The two somehow managed to alternatively block the required ports for my devices to discover each other.
plasma-firewall seems to be the main culprit since I had disabled ufw numerous times before from the terminal in hopes to make devices connect.
Never checked in the settings or I would have seen that some firewall in there (plasma-firewall) shows that its very much active.
I had set rules to allow required ports to be open in the plasma firewall too but...didn't work.

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manaya@manishitha-x451cap:~$ sudo ufw disable
Firewall stopped and disabled on system startup
manaya@manishitha-x451cap:~$ sudo ufw status
Status: inactive
manaya@manishitha-x451cap:~$ sudo apt-get remove ufw
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Starting pkgProblemResolver with broken count: 1
Starting 2 pkgProblemResolver with broken count: 1
Investigating (0) gufw:amd64 < 22.04.0-0ubuntu1 @ii K Ib >
Broken gufw:amd64 Depends on ufw:amd64 < 0.36.1-4build1 @ii pR > (>= 0.34~rc)
  Considering ufw:amd64 10002 as a solution to gufw:amd64 0
  Removing gufw:amd64 rather than change ufw:amd64
Done
The following packages were automatically installed and are no longer required:
  enchant-2 gir1.2-javascriptcoregtk-4.0 gir1.2-soup-2.4 gir1.2-webkit2-4.0 libatomic1 libenchant-2-2 libjavascriptcoregtk-4.0-18 libmanette-0.2-0 libsoup-gnome2.4-1
  libwebkit2gtk-4.0-37
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
  gufw ufw
0 upgraded, 0 newly installed, 2 to remove and 0 not upgraded.
After this operation, 4,523 kB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database ... 164046 files and directories currently installed.)
Removing gufw (22.04.0-0ubuntu1) ...
Removing ufw (0.36.1-4build1) ...
Skip stopping firewall: ufw (not enabled)
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for man-db (2.10.2-1) ...
Not building database; man-db/auto-update is not 'true'.
Processing triggers for mailcap (3.70+nmu1ubuntu1) ...
Processing triggers for desktop-file-utils (0.26-1ubuntu3) ...
manaya@manishitha-x451cap:~$ sudo apt-get remove ufw
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package 'ufw' is not installed, so not removed
Starting pkgProblemResolver with broken count: 0
Starting 2 pkgProblemResolver with broken count: 0
Done
The following packages were automatically installed and are no longer required:
  enchant-2 gir1.2-javascriptcoregtk-4.0 gir1.2-soup-2.4 gir1.2-webkit2-4.0 libatomic1 libenchant-2-2 libjavascriptcoregtk-4.0-18 libmanette-0.2-0 libsoup-gnome2.4-1
  libwebkit2gtk-4.0-37
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
manaya@manishitha-x451cap:~$ sudo apt autoremove
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Starting pkgProblemResolver with broken count: 0
Starting 2 pkgProblemResolver with broken count: 0
Done
The following packages will be REMOVED:
  enchant-2 gir1.2-javascriptcoregtk-4.0 gir1.2-soup-2.4 gir1.2-webkit2-4.0 libatomic1 libenchant-2-2 libjavascriptcoregtk-4.0-18 libmanette-0.2-0 libsoup-gnome2.4-1
  libwebkit2gtk-4.0-37
0 upgraded, 0 newly installed, 10 to remove and 0 not upgraded.
After this operation, 92.4 MB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database ... 163784 files and directories currently installed.)
Removing enchant-2 (2.3.2-1ubuntu2) ...
Removing gir1.2-webkit2-4.0:amd64 (2.38.2-0ubuntu0.22.04.2) ...
Removing gir1.2-javascriptcoregtk-4.0:amd64 (2.38.2-0ubuntu0.22.04.2) ...
Removing gir1.2-soup-2.4:amd64 (2.74.2-3) ...
Removing libwebkit2gtk-4.0-37:amd64 (2.38.2-0ubuntu0.22.04.2) ...
Removing libjavascriptcoregtk-4.0-18:amd64 (2.38.2-0ubuntu0.22.04.2) ...
Removing libatomic1:amd64 (12.1.0-2ubuntu1~22.04) ...
Removing libenchant-2-2:amd64 (2.3.2-1ubuntu2) ...
Removing libmanette-0.2-0:amd64 (0.2.6-3build1) ...
Removing libsoup-gnome2.4-1:amd64 (2.74.2-3) ...
Processing triggers for man-db (2.10.2-1) ...
Not building database; man-db/auto-update is not 'true'.
Processing triggers for libc-bin (2.35-0ubuntu3.1) ...
manaya@manishitha-x451cap:~$ sudo apt-get purge ufw
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Starting pkgProblemResolver with broken count: 0
Starting 2 pkgProblemResolver with broken count: 0
Done
The following packages will be REMOVED:
  ufw*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
(Reading database ... 163712 files and directories currently installed.)
Purging configuration files for ufw (0.36.1-4build1) ...
Processing triggers for rsyslog (8.2112.0-2ubuntu2.2) ...


Here if you check in settings you have another firewall which is the plasma one. Blast it.

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manaya@manishitha-x451cap:~$ sudo apt-get remove plasma-firewall
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Starting pkgProblemResolver with broken count: 0
Starting 2 pkgProblemResolver with broken count: 0
Done
The following packages will be REMOVED:
  plasma-firewall
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 1,379 kB disk space will be freed.
Do you want to continue? [Y/n]
(Reading database ... 163707 files and directories currently installed.)
Removing plasma-firewall (5.26.4-0xneon+22.04+jammy+release+build12) ...
Processing triggers for dbus (1.12.20-2ubuntu4.1) ...
Processing triggers for mailcap (3.70+nmu1ubuntu1) ...
Processing triggers for desktop-file-utils (0.26-1ubuntu3) ...
manaya@manishitha-x451cap:~$



Ting!!! Kde devices just saw each other for the first time.

Is it just me who somehow installed 2 firewalls? I am sorry to the devs if I am an unique case but if I'm not....
then I'm just disappointed. If you are adding a firewall of your own maybe remove the previous one? or was it needed? I vent cause I do not know.


My system?

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manaya@manishitha-x451cap:~$ neofetch
             `..---+/---..`                manaya@manishitha-x451cap
         `---.``   ``   `.---.`            -------------------------
      .--.`        ``        `-:-.         OS: KDE neon 5.26 x86_64
    `:/:     `.----//----.`     :/-        Host: X451CAP 1.0
   .:.    `---`          `--.`    .:`      Kernel: 5.15.0-56-generic
  .:`   `--`                .:-    `:.     Uptime: 35 mins
 `/    `:.      `.-::-.`      -:`   `/`    Packages: 1823 (dpkg), 19 (flatpak)
 /.    /.     `:++++++++:`     .:    .:    Shell: bash 5.1.16
`/    .:     `+++++++++++/      /`   `+`   Resolution: 1366x768
/+`   --     .++++++++++++`     :.   .+:   DE: Plasma 5.26.4
`/    .:     `+++++++++++/      /`   `+`   WM: kwin
 /`    /.     `:++++++++:`     .:    .:    WM Theme: Fireflies-dark-round
 ./    `:.      `.:::-.`      -:`   `/`    Theme: [Plasma], Breeze [GTK2/3]
  .:`   `--`                .:-    `:.     Icons: breeze-dark [Plasma], breeze-dark [GTK2/3]
   .:.    `---`          `--.`    .:`      Terminal: konsole
    `:/:     `.----//----.`     :/-        CPU: Intel i3-3217U (4) @ 1.800GHz
      .-:.`        ``        `-:-.         GPU: Intel 3rd Gen Core processor Graphics Controller
         `---.``   ``   `.---.`            Memory: 2148MiB / 5819MiB
             `..---+/---..



Removing either one of those and configuring the other one to open the required ports will probably do the job. I'm not gonna test it though, devices did not discover each other even when plasma-firewall had set rules to open the ports to anywhere. Unfortunately I did not take screenshots.

Plasma firewall is a gui end for either ufw or firewalld. It's not a standalone firewall as such. You could compare it to gufw in gnome and other gtk's, which, by the looks of your terminal output was installed as well.