I have a Windows 10 laptop computer that has a high DPI display (2496x1664). I also use several different sets of Luminosity Masking plugins and am using a Windows 10 v2004. After moving from Photoshop 2020 to Photosho 2021, I noticed that the text / icons wasn't properly scaled to fit within the module windows. Thererfore, to see everything I now have to use scroll bars for the plugin window. With Photoshop 2020, the plugin icons within the window were scaled so that you didn't have to scroll.
The specific Plugins that I am having this problem on is the Tony Kuyper TK7 Luminosity Masking tools. I contacted Tony Kuyper and he indicated that some of his users that have higher resolution displays and where the overall Windows 10 Display scaling factor need to be set to anything other than 100% this problem exists. Further, the recommended work around is to change the Photoshop.exe high dpi compatibility settings to override the High DPI scaling provided in the Photoshop.exe Properties menu. Making this change resolved the window content scaling issue but now the text / icons sizes for all of the plugins that I use are now smaller. This scaling issue was introduced with Photoshop 2021. When running the same modules on the same computer with Photoshop 2020, scaling problem didn't exist.
I also have a desktop computer that is running Windows 10 / Photoshop 2021 and the same plugin sets. On this computer, this scaling problem doesn't manifest itself. The one difference between these two computers is the Windows 10 Display text / icon scaling factor. On the laptop, the scaling factor is at the Windows 10 recommended value for this laptop which is 150%. For the desktop, the monitor is larger and the Windows 10 Display scaling factor is set to 100%. One of Tony Kuyper's other users noted that this problem only crops up on a computer that has the overall Display text scaling factor set to something other than 100%.
I don't know if this is a Windows problem or a Photoshop problem but it only occurs with the new Photoshop 2021 version. Hopefully this will be addressed in a future update to Photoshop.