If you happen to be paying for iCloud storage, you could use their hide-my-email service for those rare accounts and have it send to your proton email (apple lets you use an external email to forward to). That’s one of the big benefits of apple’s alias solution; they are all in the icloud.com domain and no website would ever block that.

I don’t have an answer to your specific question, but honestly I think learning to subscribe to a community is a really important “tutorial” on using lemmy/reddit. Otherwise they might not understand how to get to each one. You also could just have them look at the local feed so they wouldn’t even need subscriptions.

I personally haven’t used it yet but I believe you can do all this with Matrix (choose your client - probably Element).