TYPO3 9.5.22

I have a TYPO3 based site with a number of department related subtrees, D1, D2, D3.

Users of department D1 are in backend group D1 and can work in the D1 Subtree via a DB mount.
Users of department D2 are in backend group D2 and can work in the D2 Subtree via a DB mount.

If a user U1D1 (Member of Group D1) creates a page in the D1 subtree, the page group owndership by the "admins" group.

This means that U2D1 can not edit pages of U1D1.

What do I have to do so pages created by U1D1 belong to group D1 instead of admins?

Any help would be greatly appreciated.