#8634 is specifically about a breaking change that occurred in v12. It's literally the first line of what you linked:
> In the v12 release of Forgejo (fixed in v12.0.1) there have been breaking changes that impact third-party authentication sources that use Forgejo as a provider. If you have been affected, please help us assessing the impact ...
There also was feedback saying approximately that they've been burned by security changes in the recent past and don't want to run into similar issues without due consideration.
and there is open issue for that discussion https://codeberg.org/forgejo/forgejo/issues/8634