v1.24 is now available
Brotli, GZip, and Deflate compression are all supported by default.
There are also settings to tune the compression levels and eligible mime-types.
https://help.supersimpleserver.com/config in the first section, about 1/5th of the way down the page, has the full list of settings if you want to really customize the behavior. But the default settings are pretty good.
Still working on QUIC and some of those other things... to be continued.