Ive read - and indeed sympathized with - what has been written here.
Rather than write a long winded rant, I will try to keep it short...
I too struggled with the same problems that you did, but found a working solution (for my purposes at least):
1. I have a Debian Linux laptop for internet use and file downloading but also any apps that are available for Linux (i.e. Hatari, Relaunch64, etc), as I generally dislike the later iterations of Windows.
2. I have a Windows XP laptop for my game engine development. This machine has been OFFLINE since its Windows installation process 10+ years ago.
I guess you could do the same with a 'static' installation of W98, NT4 or whatever OS your old legacy apps needed to run on.
Whilst it may be a minor inconvenience to transfer the odd file over by USB every now and then, I dont have to worry any upcoming OS updates trashing any programs or data I may have on the machine, or hackers snooping in my files. You can tweak away, changing things to exactly how you like them and they will still be in the same static (working) state YEARS later!
Im perfectly content with this setup, but then again, I prefer the 'spartan but focused' workdesk. i.e.:
* Im happy to use a £10 phone with just a snake game, rather than a modern smartphone. (Dont feel the need to have more than 3 methods of electronic communication).
* I tend to use Devpac 3 instead of all the modern 'feature rich/overwhelming' cross platform editors.
* If I could have apps run on the 4 colour GEM desktop, I would use that instead; I dont like over complex desktops.
I suppose its kind of like how I get my best ideas when in the WC!

Theres less to distract in there and it actually does seem to increase the cognitive sparks!
Of course, it all depends on what you need out of your work environment.
Anyway, I'll leave it at that. Maybe give that setup a try
@exxos ?