Proton Pass has a similar feature, I love it. But Spotify had banned my account and asked me to email them from the alias to unlock it, which is not possible. So you should be careful with that. A lot of companies employ anti-privacy practices.
You can login to the SimpleLogin.io interface and setup reverse aliases even if you create them in proton pass. They don't have the integration fully down yet so it's clunky but it works.
Were you using simplelogin.io, which is part of Proton? It is actually possible to reply or send mails from the aliases you create there. The feature is called reverse-alias.
If you’re talking about a SimpleLogin, you CAN email from it. I forget the exact terminology (I can check if you need) but you can generate a forward address that you email and the receiver (Spotify) will see it as If you have emailed from your forwarding address.
Anyone signed up for one of Relay's paid subscription options will also be able to reply to emails anonymously . . . A free account will allow for up to five email masks and remove trackers for you, with additional protections available for paid subscription tiers.
DuckDuckGo has the best free solution ATM IMHO, if you don't mind the RNGd names: "unlimited" aliases, reply-ability, and trackers removed.
I mean I won't use it because I don't trust Mozilla with full access to all my websites, but I like that they have some monetization build in so that they can diversify the income and not only get money from Google.
But I still think that Thunderbird is doing it better by asking for donations.