I have no real answer for you, but Windows 7 is now a 14 year old OS (released in 2009), has been out of mainstream support for 8 years now (2015) and extended support finally ended in January 2020 roughly 3 years and 9 months ago.
What this means for any software/hardware company including Paradox is that THEY TOO can no longer call Microsoft for support. So if they have a problem with Windows 7, Microsoft will tell them: Oh well, that OS is now as obsolete as the iPhone 3 (which was released in 2009 as well), so we won't support you.
That the OS is "perfectly fine" and that your old iPhone 3 with them sweet rounded corners is also "perfectly fine", despite both of them being 14 years old..... doesn't really matter, as the companies providing support for these products pulled the support on it a LONG, LONG time ago.
There will come a time (and it has already happened with many other software companies) that companies making software products will be unable to support Windows 7. It is very possible that Paradox no longer has a single Windows 7 computer left in their building to even test the client for Windows 7, and the fact that it still worked up until now..... is just pure luck because the code had not changed all that much, or not in the spots that matter for compatibility.
I'm not saying this IS the cause, but running a 14 year old OS is bound to cause problems at some point. Perhaps its time to upgrade to Windows 10, which is still supported for another 2 years....