My galaxy themes has been working ng weird latley. Ever since I got a new version if android, my themes only change the wallpapers and icons. Everything else us just white. I do not have dark mode on so that's not it. I hope Samsung fixes this soon!!! Next I try to apply an icon and it says it is not for my version of android and some things may look funny. Is Samsung working to correct this.
I have the same problem. I upgraded from a Galaxy S7 with Android 8 to a Galaxy Note 20 Ultra with Android 11. It turns out that a lot of theme designers have not updated their themes for the new Android version. My purchased themes migrated to my new phone without any problem. Some themes did update (kudos to those designers) and others did not. I lost over 65 themes, but some that had been made for Pie work pretty good. I only lost the keyboard theme and themed contacts. Also the phone keypad list is black text. Also, if the theme is in your purchase list but not for sale in the Theme Store, it will show white while applying. Your best solution would be to contact the theme's designer to find out if they have plans to update the theme. I ended up deleting over 30 themes from my purchase list. I don't think Samsung can do anything about this as the designers have to keep up with the changing operating systems.