I had big problems running Lemmy 0.19.1 and Nextcloud together on the same server. Each for them worked nice, but when they run together they hogged so many resources that I had to stop one of them. In addition to that there was the problem of my posts and comments not being federated correctly. Sometimes a restart would help for a while but then it would stop again. That's not fun when you're the only person on a server and no other server can see what you wrote. That made me use lemmy much less to be honest.
Anyway, let's see if 0.19.2 fixes some of those problems. I have a workaround for the load problem, I'm trying to switch from Nextcloud to Radicale for CardDav and CalDav and from Nextcloud to Syncthing for file syncing. And in the release notes they promis that they fixed the federation problems, so I'm hopeful.
Well, good luck. Nextcloud is quite heavy if you need a basic sync and *Dav capabilities.