This is wonderful! Texel Raptor, developer of the absolutely fantastic theme park building game Parkitect have announced a new Beta is available that brings in cross-platform online multiplayer.
In the current stable release, the online multiplayer which is relatively new is locked per-platform but they did say since it was added they would be exploring how to get it all synced up across Linux, macOS and Windows. This fresh Beta was released yesterday April 1 (it's not an April Fools), which any owners on Steam can opt into and test it out.
Texel Raptor say that if the tests go well it will "become the new default version of Parkitect in a few weeks, so if you are interested in cross-platform multiplayer please give it a try and let us know if you encounter any issues".
Having cross-platform online play is pretty essential, especially for Linux players where it's a smaller pool to play with. Thankfully it's all becoming a bit more normal.