Adjustable Scrollbars-thickness breeze-/dark, HDPI, scaling, 10-Bit-display, png-icons.

I can't decide if this is an idea, a complaint or a bug but... for sure I know that, for a flag-ship-theme like "breeze" it's a "no-go".
Scrollbars:
Since at least 16.04 (4 years) we have "plasma5" with breeze and still haven't resizable thickness for scrollbars, these, with a 4k-display are almost impossible to catch. The feeling is like under Win3 on notebook with 10 MB-HDD. I wonder if no one has addressed the issue and... due the fact that almost everybody offers KDE as DE... how do all other "providers"? Still use all KDE4? Or drop KDE like Mint?
It would be great if a kind of `qt5ct` directly integrated in `systemsettings5` with the possibility of GTK-scrollbars-scaling.

I read somewhere to use part of "oxygen" with breeze-dark to resize the scrollbars under KDE5, manipulate Gtk3.css for scrollbars under gtk but still not works with all apps and nobody explains how-to for newbie. "Qt5ct" cannot help to resize gtk-scrollbars and many apps have/use own "css". I read also Qts-documentation is incomplete. Kvantum offer help, is low-rated and... again, nobody explains how to work with. Sorry! That is not freedom, that's chaos.

HDPI:
Enabling this in "file:///etc/sddm.conf" works in part under "x11", to big under "wayland". What "SDDM" really do or is for, i don't know. Sure is that if i want see anything by "Login" i must do it. Arch-Wiki say to do it under `/etc/sddm.conf.d/` but i haven't it, maybe should i install Arch.
TTY is unreadable if i don't make special adjustments, the same is valid for GRUB. A newbie should have a small display or find a geek.
Switching `PLASMA_USE_QT_SCALING=1` in `/etc/xdg/autostart/org.kde.plasmashell.desktop` or `~/.profile` or `/etc/profile` cause horrible flickering not only in Kubuntu 18.04 but also in 20.04. I don't believe the fairy it will work with higher plasma-version. The only one thing... under wayland is less flickering. My last tray will be to insert `export PLASMA_USE_QT_SCALING=1` or `export PLASMA_USE_QT_SCALING=true` in `/etc/environment`, if even this will not work... maybe we must wait for wayland to be finish.

10 Bit:
I have a 10-bit display and my GPU can more than this, i read also (Arch-Wiki) where this parameter can be set in `x11` but it will crash.
Is there any chance to get `x11` working with 10-bit depth? Or this will be remediated only under wayland? And... do you know (perhaps) when wayland is finish?

PNG-Icons:
Is not antiquate to still use png-icons instead of `svg` or vectorized-icons anyway?
If the future is "every pixel will be perfect", i don't think png will be the future and... honestly spoken, a vector can be increased and reduced at pleasure and don't need to collect ton of icons in different size that disappear when someone chooses a size not stored in `systemsettings5`.

We are behind (I think). What GTK makes, interests me less. If I can help... I like to do that. If necessary, contact me, even if I am a newcomer.

In the meantime, i would be glad if someone can suggest me at least a temporary solution for all this small and big "problems".

Thanks in advance for reading and maybe help & thanks to all developers made/making kde.

Best regards.

dear advantagedtony,
I can confirm the "pain in the ****" with the scrollbars.
4K hidpi-screen on the 15" notebook, Manjaro (based on Arch) with KDE Plasma 5.18, Breath2 Theme.
My main applications are Thunderbird, Dolphin, Waterfox and Code - OSS (VS Code?). Only Code shows a decent width for scrollbars. The other applications present those ultra-thin stuff. I did a deep dive the whole evening today just to learn that there is no quick win for the objective "scrollbars with more width". Even editing gtk.css in the chapter "Scrollbars" was without result.
Only the Oxygen-Theme offers a setting, but I hesitate to switch back from Breath2 to Oxygen.
br
chris
p.s. I want to thank all the developers who keep KDE running and evolving! And after all the stuff I found about scrollbars: hell, this is a complex stuff.