I signed up for protonmail ultimate hoping to use the unlimited hide-my-email aliases, but was disappointed after attaching my custom domain that I couldn't then use it in the alias generator (either the one build into proton mail, or the proton pass one which are the same). I might be able to inconveniently add a subdomain to simplelogin, but it would be really inconveniant compared to the protonmail/protonpass integration.

I have a custom domain for ProtonMail and would like to use it to create my aliases in Proton Pass.
I do not want to configure another service (SimpleLogin) for this purpose !

You need to add your domain to SimpleLogin, since ProtonMail itself doesn't provide alias functionality.
Then you can use the domain is PP too.

With the growing popularity of Proton Pass and Hide Me, more systems will detect and block hide-me domains. To bypass this, offer the option to create an alias using my own domain.

It would be great if we could create email aliases using our custom domain directly through ProtonPass. I know this can be done via SimpleLogin, but thinking about a family plan where a spouse or children would use the service, it's complicated to deal with privacy education by asking them to use one portal to create emails and another to create and manage passwords and logins. Even for personal use, it's much simpler and faster to create aliases through ProtonPass directly via the app or extension.

Along with this, it would also be great if each family member could create their own aliases on their accounts using the custom domain of the family owner and each receive their emails related to their created aliases.

It would be great if we could create email aliases using our custom domain directly through ProtonPass. I know this can be done via SimpleLogin, but thinking about a family plan where a spouse or children would use the service, it's complicated to deal with privacy education by asking them to use one portal to create emails and another to create and manage passwords and logins. Even for personal use, it's much simpler and faster to create aliases through ProtonPass directly via the app or extension.

Along with this, it would also be great if each family member could create their own aliases on their accounts using the custom domain of the family owner and each receive their emails related to their created aliases.

Yeah, there are already some websites that have blocked @passinbox.com and @passfwd.com. Would be great to have any solution for this problem!