I am not trying to convince you of anything, and you have the right to hold to your contradictions, but I find this at odds with most proprietary software, even more so if their execution environment isn't stable or 100% under control.
Regarding your specific needs, it also does sound a bit like the XY problem: you don't really need an app (unless locked-in by data you can't migrate), you just need the functionality it provides, though that may require some unlearning first. Oh and yeah, of course there aren't alternatives for everything.
But if you are really locked in and see the writing on the wall for your solution, you always have the option of creating your own migration path, or a stub application that does the bare minimum you need. Other might step in and help you, so it might be worth asking around first.
From my point of view, Linux is not broken at all. It runs the software I need (I'm comfortable with Gimp, I don't have spreadsheets that pass the limits of LibreOffice and I don't use EA). Lately, the move from X to Wayland has been introducing some brokenness - it's not as easy as it used to be to run X apps across the network - but I imagine all these will be eventually fixed.
Like you said, most users don't worry EA is Windows-only because most users don't worry about things like OS.
My needs are far from average though, as I mentioned in the post. Not sure its spreadsheet editor would even recognize what's happening in my Excel files.
And again, I emphasized "software of that class" for a reason, because migrating "easy stuff" like productivity tools to Linux/Mac was not a hassle. I'm sure there's ton of new promising modeling solutions, but I can't stop using Enterprise Architect because of literal vendor lock. I use automation and I use code generation, which is implemented through .NET API (not .NET Core), which assumes Windows. However, I suppose, 99% of EA users don't worry it's Windows-only, for many enterprise-class solutions OS is just a wrapper for the software.