They already have the functionality built in, with passkeys. All they would have to do is do the same thing. Have you click the login if you want to tie it to that (or vice versa, tie the login to the alias) and it shows up as one entry.

As someone who came to Proton Pass with well over 300 items from a chronic bad habit of importing and never cleaning anything up as I had bounced around between PW managers, I support this option as a QoL improvement.

My idea would be the ability to select multiple entries, click a link button, binding them into one complex entry with an unlink button if you need to add or remove specific entries. And by linking the entires, it should hide all but the one linked entry from search and being listed in "All Items" and whatever vault it's in reducing the number of entires and simplifying housekeeping.