They block some user-agents, maybe that's it?

From [1]

> We must regularly implement temporary security measures to ensure the availability of Codeberg's resources and prevent abuse.

> The 403 you have received is expected based on the UA.

From [2]

> What is the version of your chromium? AFAICT <=137 gets 403 Forbidden: [...] while >= 138 works ok: [...]

[1] https://codeberg.org/Codeberg/Community/issues/3084

[2] https://codeberg.org/Codeberg/Community/issues/3078