I’ve found this a good tool for searching communities: https://lemmyverse.net/communities

Others have covered the practical use knots, so I want to throw a couple fun ones out there:

• Double carrick bend
• Monkey’s fist

If you’re into crafts, friendship bracelets use half hitches. Macrame and tatting are also variations on tying knots in patterns.

There’s !imadethis@lemmy.zip for any hobby that produces something, but that leaves out the activity-based hobbies