That is not yet decided, maybe some and not all apps will receive an update to continue working with PHP 8+.
They are usable with 20.1 and upcoming 21.1 by installing the old 14.3 packages. Which work with PHP 7.4, but not PHP 8.0.
As I wrote above, you can use the old 14.3 egroupware-epl-wiki or egroupware-epl-phpbrain packages, or you can clone them into /usr/share/egroupware on your host. The (re-)starting container integrates them into the new versions. To clone them using master branch you also get PHP 8.0 compatibility for wiki and knowledgebase (work in progress):
The final 21.1 release will be with PHP 7.4, not yet PHP 8.0.