I am currently evaluating Pop! OS (Ubuntu-based) as a potential replacement for my home computing needs. As a result, I've been going through all my current workflows in OSX and ensuring that viable alternatives exist. So far, that looks promising.
The biggest question mark on this list is the viability of Scribus. When I last explored it as an option in 2017, I discovered an odd "feature" whereby Scribus would ignore fonts on your system that did not meet some esoteric standards for font file "correctness." Sorry, but if I paid money for a font and every other application on my system is able to use it, I expect my print layout software to be able to use it, too. Fortunately, as per my fiddling with the most recent version of Scribus, this appears to have been corrected. All fonts on my system now appear to be usable by Scribus. There could still be some other gotcha hidden within, however.
This weekend, I will be attempting to layout The Shipwright and Other Stories in Scribus. I already have a complete InDesign layout, so the goal will be to see if Scribus can duplicate that work. If that proves viable, I will be good to go to migrate off of OSX.
In my next post, I'll talk about changing over from Scrivener to Manuskript, in which I encountered minor obstacles, but on the OSX side rather than the Linux side. Manuskript is shaping up to be a much better tool than Scrivener ever was... and Manuskript is the free option.