Kaybee
It works out oft the Box, if you add your Forgejo Account as a Gitea Account. This also makes sense, because Forgejo is a Fork if Gitea. Tested in 1.12.3...
Could not reproduce with current Aristois: Which platform are you using ? Paper Versions of Negativity and of the server Negativity 2.7.1 Paper 1.20.2
I had the same Issue but figured it out thanks to @NotActuallyTerry after some time. For the mapper "User Property" did not work, but "User Attribute" did. I'd like to...