Does Windows 11 hide its font files?

[Ofnuts]

You have to either restart Gimp or refresh the fonts in the Gimp font list (open the list, hit the < icon at top right, then Fonts menu > Rescan fonts list).

If that doesn't work, you can try this:

• With your file explorer, navigate to C:\users\{your id}\AppData\local\fontconfig
  

• Erase the directory contents (in partocumar the cache subdirectory)
  

On next start, Gimp will rebuild its font list.