"There was a problem connecting to the server" "The server may not exist or it is unavailable at this time. Check the server name or IP address, check your network connection, and then try again."

File sharing broke after upgrading 2 computers to Catalina. I spent days trying to figure it out. I tried so many suggestions (including fresh OS installs), all to no avail. I have fixed IP addresses on two home computers (Macbook Pro and Imac). One machine could connect via SMB to the other but not in the reverse direction. I'm sharing the solution that I found via my own exploration (and which I didn't find elsewhere). On the server (Imac I couldn't connect to), I went into System Preferences > Privacy & Security > Firewall > Firewall Options . I changed SMBD to Allow incoming connections.