Roundcube and SOGo (which is used by Mailcow, but hass fewer features than Roundcube) are the only somewhat modern looking options. All the other stuff looks like straight out of the 90s/early 2000s. Nextcloud Mail is pretty good as well.

That’s what I thought when I first saw this

Absolutely

You can play Stardew Valley in multiplayer co-op mode, it’s also quite cheap at $14, it’s available on every platform and even has excellent Linux support