I know we are supposed to use the UI, but it’s not ready for all purposes yet. Therefore it is nice to know that you can force the classic view for a little while longer. If for some reason you can’t use this approach, you can also change the URL like Jamie Bowman mentions here
https://admin.powerplatform.microsoft.com
Open Environment and then behavior and change the variable
The result is that you now can open the Customize to classic. This doesn’t force the other UI apps to classic, so you are still all good:)
CRM Keeper 