This is a very old thread, and Ubuntu MATE 20.04 is years beyond it's EOL (refer Ubuntu MATE 20.04 LTS reaches end of life), with even Ubuntu 20.04 LTS beyond its EOSS (refer Ubuntu Fridge | Extended Security Maintenance for Ubuntu 20.04 (Focal) began on May 29, 2025) so you're mentioning a release that shouldn't be used on networks or online.
Ubuntu MATE is a desktop release; thus follows the [ssh] standard of Ubuntu Desktop; that standard differing to Ubuntu Server and Server defaults
If you're using Ubuntu MATE on a Raspberry Pi, I suggest you instead install a supported release of Ubuntu MATE (or install Ubuntu Server and then add the MATE desktop onto it)