I stopped using Liftoff so someone else may be able to better describe it.
I used to have this account and beehaw signed in. When viewing my combined feed I would be commenting and voting from this account unless it was a beehaw post (as they defederated) where it would use my account there. Basically whatever account loaded the post would be in control.
This was nice with two accounts but I also had a lemmy.world account that I don't use and if I had it signed in to Liftoff any time I commented on a post from a lemmy.world community it would automatically make my comments come from the account I never used.
The difficulty is around handling what account to use. If the current account is used regardless of which post you tap then this is easy.
This is what I would have liked. I prefer to use one account unless there's a reason I can't (such as defederation) however I wasn't an active Liftoff user for long so it may be better to poll the liftoff community and see what'd they'd like. The dev has been MIA for months so I wouldn't feel bad doing so.