Problem with sharing folder with group

Ver 18.3.0
I created a folder ant want to share with 2 groups
already created and users assigned

When I put in the field the name of the group or username nothing is found

When put in A
admin appears

NOT as shown in this instructions

Something wrong in settings??

There is the problem

But how is it possible to allow admin group to share folders to all groups
BUT allow users to share folders only in their Group!!?

Other user in his group NOT admin also here!

Just take out that option. If you allow users to only share inside their group, you allow them to share with every single user in that group, but they can’t share with the group itself.
That might well be a design bug = open a github issue if you need to have it changed or submit a PR.