Permalinks in Multisite not working when Main Site is in a subdirectory

[francwalter]

Hello
I have installed WP 6.0.2 on my Server in a subdirectory
/var/www/example.org/wp
After install I activated Multisite.
I added a website "example2" to the main site and permalinks are working, e.g.:
example.org/wp/example2
Sites are found as e.g. example.org/wp/example2/subsite
Then I used an own domain example2.org instead of example.org/wp/example2
and now the subsites of example2.org are only accessable with Permalinks > Simple (e.g. example2.org?p=123) but not with subsite names (e.g. example2.org/subsite).
This seems to me a bug, as it should work since WP 3.5 as I read in doc.
Thank.frank