Yes it’s an API token.
For anyone looking for getting a Maven repo up and running (v1.23):
Enable Maven package in app.ini:
[package]
ENABLED = true
[package.mvn]
ENABLED = true
Restart server.
Then configure Maven locally following Maven Package Registry | Gitea Documentation
The access token is generated in User settings > Applications. Set permissions > package Read and Write (not sure if required).
I used an organization as owner.