Here’s a step-by-step guide on how to follow this Lemmy community from Mastodon, using the Web interface.
Step 1: Copy the URL of the Lemmy community you want to follow. In this case: https://sh.itjust.works/c/opensim
Step 2: Go to the website of your Mastodon instance.
Step 3: Paste the copied URL into the search field in the top left corner.
Step 4: Hit Enter.
The search should now show the community as the only search result.
Step 5: Click the follow button much like you’d follow another Mastodon user.
Congrats, you’re following this community now!
This should have appeared as a post in the Lemmy community @OpenSim. For some reason, it didn’t. At least I can’t see it there.