Mask function button not working

Thank you Axel-M.  Your first method worked.  I suspect it has something to do with the AMD driver for the Radeon 780M igpu on the Ryzen 9 7940HS processor..

The first thing that you should try is to switch off the GPU support from the Lightroom preferences and check if that helps to fix the issue.

Go to Lightroom > Preferences > Performance tab > Uncheck "Use Graphics Processor" > Restart Lightroom.

https://helpx.adobe.com/lightroom-classic/kb/troubleshoot-gpu.html

If Lightroom doesn't start correctly the please see "Solution 2" in the document behind the link below.

Troubleshoot GPU issues | Lightroom Classic (adobe.com)

Another step is to try to reset the Lightroom preferences.

https://www.lightroomqueen.com/how-do-i-reset-lightrooms-preferences/

It's recommended to backup your preferences before you reset the preferences to the default settings:

https://helpx.adobe.com/lightroom-classic/kb/preference-file-and-other-file-locations.html

If this doesn't help we need more informations about your environment including the following:

• Adobe product and version number
• Operating system and version number
• The full text of any error message (s)
• What you were doing when the problem occurred
• Screenshots of the problem
• Computer hardware, such as CPU; GPU; the amount of RAM; etc

Please provide also a copy of your 'System Info'. This can be get from the LrC Help > System Info menu item. There's a copy button in the System Info dialog. Press this button and paste the info into your next forum post.