But I can't see any place on lemm.ee that lets me subscribe to it from my lemm.ee account. I searched for it under Communities, but it doesn't show up as an option.
Click the hamburger icon in the upper left (talking as if you are in mobile web)
Go to communities.
The page always lists your local communities first, click all.
In the search box put the full address. It looks like, !name@domain.tld. For example, !cats@lemmy.world
Hit search and wait patiently for up to 15 seconds. Important.
You will see the community show up (unless it's blocked) and you click the link it shows you.
I don't believe Squabbles is federated/using ActivityPub, so you can't connect to it through Lemmy. We can connect to Lemmy instances, as well as some other ActivityPub communities (most notably Kbin and Mastadon instances), but Squabbles is not using ActivityPub, it's an entirely separate social media.