Can't add pictures as new bullets in MS Word. Bad Request-Request too long

When I try to add pictures to define a new bullet it shows "Bad Request - Request too long / HTTP Error 400. The size of the request headers is too long."

It doesn't matter if I do it from the bullet button in the ribbon, or defining a new list style. I don't have that problem when adding a regular picture or even icons.

I've tried:

1. Deleting the ListGal.dat file as suggested in another post
2. Replacing the Normal.dot global template file as suggested in the same post
3. Clearing the officefilecache folder
4. Going offline (the same window appears but blank)
5. Repairing through the Windows repair option

I'm on Windows 11, using the desktop app. I was using MS Word version 2312 (Build 17126.20132), and just before writing this post I checked for updates again (I had already tried a few days back with no success) and it actually updated to Version 2401 (Build 17231.20084). I opened Word the Bad Request didn't appear. I opened a new file and tried again and the message came up again!

I hope I gave enough information!