The Adobe Color Themes panel is cut off on the right side. There's no left-right cursor when I hover over either the left or right sides. It expands up and down just fine. Other panels work just fine.
I used Alt+Control+Shift to reset my preferences and that didn't fix it. So right now everything is the default settings.
Which version on which system is it?
Sorry, it's Illustrator 25.1 64-bit on Windows 10.
If you drag the panel out of the dock, does it work better then?
No. It still only lets me resize it vertically.