Sometimes it takes a long time for the users to appear in Dynamics 365, even though users have the appropriate licenses.
E.g. here we have added user6 in Microsoft 365 Admin Center.
Back in CRM, we do not see user 6 added.
One way to add the user is through Force Sync User action of Power Platform Management connector.
or the other option is to ask the user to log in to the Power Apps.
As soon as the user logs in we can see his account added/synced to the enabled users in CRM.
Thanks to Emre Gulcan for this trick
Hope it helps..