Hi,
A friend of mine showed me this problem asking if I have a solution for him but it surprised me and couldn’t help him.
If the resolution scaling is set below 100% then it prevents from maximizing any app windows. Tiling to half screen or to a corner is also broken in such case. Scaling above 100% works fine.
It seems to only affect Wayland, however. My SteamOS with X11 doesn’t have this issue.
So not sure if it’s more of a KDE thing or Wayland thing.
Any thoughts?
This appears to be a known coordinate calculation bug in KWin (Wayland) when dealing with sub-100% scale factors. In Wayland, the compositor handles the geometry differently than X11; when scaling below 1.0 (e.g., 0.75 or 0.8), the math for window constraints often hits rounding errors that break maximization and tiling logic.
Since you’re seeing this on Wayland and not X11, the most stable workaround right now is to keep the global scale at 100% and manually lower the Font DPI instead:
This achieves the ‘smaller UI/more space’ effect without triggering the compositor’s scaling bugs.
If you have a moment, it would be worth filing a bug report under the KWin product. Despite being a known issue, things are typically prioritized based on how many people they are affecting. The more people there are reporting the same thing, the higher the need for a solution becomes.
I have the same issue on Wayland.
This is actually the primary reason why I haven’t switched to Wayland yet and why I’m still using X11. I need scaling to work below 100%. I don’t want to change my fonts.
I have the same issue,
Especially on apps that use chromium, it started with chrome from about last year now last week Spotify also started having the same issue.
@Hardware_Accent, please don’t forget to mark the thread solved if my solution fixed your problem; that way other users will know what they need to do. 
I’m also experiencing this issue, and it is making the desktop really difficult to use. When I set the scaling below 100%, several apps stop behaving normally. Some won’t maximize, others cannot be resized at all, and a few do not even render their UI properly. It feels like the window manager and the applications aren’t agreeing on the actual window size. I’ve tested this on both X11 and Wayland with the same results as OP. Really hoping this can be looked into, because right now anything under 100% scaling breaks basic window functionality for me. I have one monitor that I want on 50% and the rest on 100%.