You don’t need different accounts. I have an account in Mastodon where I follow a community from Lemmy for example.

The thing is you have to manually search and follow communities and people from other services.

So if you go to Mastodon search bar and type “@linux@lemmy.ml” for example, it will show you the community content as a Mastodon profile and you can follow it and see the posts on your timeline.

Does the PWA shortcut auto-updates or to use a new version I have to delete the shortcut and create it again?

There’s a very good post from the RedReader app developer (another open source Reddit client) about this issue for their app: https://old.reddit.com/r/RedReader/comments/132qkb8/update_2_reddits_proposed_api_changes_and_the/