It is.

Bitwarden integrates directly with several email alias providers: https://bitwarden.com/blog/add-privacy-and-security-using-email-aliases-with-bitwarden/

What do you mean by that?

True, but that’s defense by concealment. If they notice the domain, they can block it without harming their business. My argument is that iCloud is too large for them to block.

There are other options for email aliases. iCloud has a pretty robust system, and its ubiquity makes it less likely to be filtered.