FediDB can be used to share server recommendations by query params.
Open Loops servers: https://fedidb.com/software/loops?registration=open
Open + Mature Lemmy servers in NA: https://fedidb.com/software/lemmy?region=north-america®istration=open&mature=1
Open + Mature Mastodon servers in Europe: https://fedidb.com/software/mastodon?region=europe®istration=open&mature=1