One of the developers (bartwe) has responded to comments on the games Steam Discussions page saying:
We checked out Proton but currently .net games aren't supported by it.
Staxel uses FNA currently, one blocker is Chromium which we use for UI rendering and issues with mono not supporting and/or having bugs in some of the libraries that we use.
Compatibility Report
System Information
I confirm:
steam-405710.log
Symptoms
Requires dotnet40 to be able to work.
Notes
One of the developers (bartwe) has responded to comments on the games Steam Discussions page saying:
(It's the last post on the page)
https://steamcommunity.com/app/405710/discussions/0/1693785035830392508/?ctp=2