KDE Neon 5.23.2
Intel CPU
NVIDIA GPU
32 " 4K screen

Problem: any chomium based browser works fine on a 100% scaled 4K monitor. But when I scale to i.e. 150% or 175%, then the Chrome/Brave/Edge etc. browser keeps getting smaller after opening a new instance. Manually dragging to a bigger viewport does not work. Chrome keeps scaling itself down til only the title-bar is visible. Firefox is working fine.
It happens one two different machines with different specs, but both with a 32 " 4K screen and a nvidia card.

Is this a Plasma bug and is there a solution? Or does it have to be addressed by Chromium build browsers?

It has nothing to do with KDE NEON of PLASMA. I just installed a brand new Fedora 35 (GNOME) on a spare HDD from the same computer and it happens there to on 200% scaling. (Fedora does not present fractional scaling). So I have to report a bug for Google Chrome Stable.