All o365 migrated users are able to list whole AAD directory when logging on azure portal. I think this is common since AAD is migrated to new portal. The current aad has no subscription activated (only used for O365), it's not possible to log on classic portal because there is no subscription. Is there a way to block this view for "normal/regular" user (roles)?
Thank you that's true, but I don't expect "regular" user to use PS to obtain info. I would assume these settings are disabled by default for at lease user roles .. as well as adding new App Registrations.
It is the same as your OnPrem AD - by default the whole directory is available as read-only to any authenticated user.
If you are not concerned about average users using Powershell, then I'd suggest you also not worry about average users using the admin portal and finding the right blade. Both are equally easy to do - but also equally unlikely for a standard user to stumble across.