I am used to google searching “[THING] site:reddit.com”
Might pick a few good representative instances on lemmy, mastodon, etc, then make a compound search:
site:lemmy.ml OR site:mastodon.social [thing]
then set up a search keyword like fs
for it so you could type fs [thing]
Depends on the browser. In FF it’s part of a bookmark. In Chrom* it;s under search engines. more info