I thought one of the advantages of the Fediverse was to have one account but access to many services. Is this possible just not common? I already have a Lemmy account and Mastodon and I didn’t want to start making more just to try out the other services.
It depends on whether the services are compatible. They don’t all implement activitypub quite the same way.
You can try pasting something into the Lemmy search field (a Mastodon user, pixelfed feed, etc.) and see what comes up. But it may take a minute to federate the first time.