I bought 1st part "Old North" with DLCs and am playing on Linux.
As "Clestia Tales" is a Saga I think 2nd part is started with Windows but Linux will soon follow.
Or are there obstacles so a Linux port of "Realms Beyond" is not planned for the foreseeable future?
I could not find any answer on the web ... so any clarification is welcome!

Indeed, the situation seems unclear. It seems it was supposed to be on Linux (like Old North), but so far I haven't found anything definite yet. Maybe it is delayed... but then, sometimes those delays mean "never". :(

The kickstarter, however, states that Linux is to come, so if people funded they should also receive. (Sometimes on GoG it's a licensing issue for the main game was made by company X but the port was done by Feral and needs extra negotiations.)

Sorry I'm a bit late here but I found a thread on Steam where the developer replied. Sounds like they are not going to port it to Linux. https://steamcommunity.com/app/684700/discussions/0/2292842508228951235/

Thanks for pointing to this thread. Oh, well. Or not so well. They should at least refund the Kickstart backers. And moreover, it's hard to tell actual numbers of players on operating systems. E.g. gog sales are for all platforms, you buy once, you got all 2 or 3 binaries. They'll hardly be able to tell that apart.

Well, that simply means no purchase for me, no money for them. :p