After running system updates this morning, the X11 session of Plasma that I usually use no longer shows any title bars or window controls for any program I open. It doesn't seem to matter what it is. Chrome, Slack, Dolphin, and more are all missing them. Kinfo shows I am running Plasma 5.24.5 and KDE Frameworks 5.94.0. If I run the Plasma Wayland session instead, the title bars are there, but it has its own set of other issues which is why I don't like using it. Any and all help is appreciated.

Same here! Also missing virtual desktops, various keyboard shortcuts do not work, and latest opened window stays on top despite clicking on parts of a previous window.

UPDATE:
Running "sudo pkcon update" gives following output. Guess something went sideways during dependency resolution in Discover and "kwin-common" sounds important....

Fatal error: The following packages have unmet dependencies:
liblcms2-utils: Depends: liblcms2-2 (>= 2.12~rc1) but 2.9-4 is to be installed
kwin-common: Depends: liblcms2-2 (>= 2.12~rc1) but 2.9-4 is to be installed

Had the same issue. Looks like it is related to none-availability of liblcms2-2.12~rc1xxx:i386 in neon user repository. Found https://forum.kde.org/viewtopic.php?f=309&t=174973 this post but the mentioned solution didn’t fixed the issues on my machine.

Instead I fix the issue on my machine like this:
But please note: With this solution I had to sacrifice i386 tools like wine:i386 for for now!

- Check for available versions of liblcms2:

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 apt policy liblcms2


- Force install required 64Bit version of liblcms2 (required by kwin-common package) This step will remove some i386 packages as dependency resolution.

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sudo apt install liblcms2=2.12~rc1xxx


- Force reinstall kwin, kwin-x11 and kwin-waylaid to fix broken setup:

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sudo apt reinstall kwin, kwin-x11, kwin-wayland


- reboot and now I had my normal behaving/looking X11 and Wayland desktop back.

I had the same problem this morning and none of the suggested fixes worked for me.

In desperation and cluelessness i just tried:

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sudo apt install kwin-x11

And it all seems to working again. Hope this helps.