If you're having trouble with joining servers or sharing to LAN, this thread should help by providing some solutions for common causes. This is my first time writing a comprehensive troubleshooting guide on this forum so if you have any feedback please let me know.
1. Hosts file
What's a hosts file and why should I care?
How do I fix it?
How do I know if this worked?
Repeat the steps above and check if the changes you made to the file have applied.