See the ongoing discussion here:
https://www.mobileread.com/forums/sho...d.php?t=245069
As about four threads have already been merged into that one, if a moderator sees this, maybe this one too should be merged?
If you want to run unstable software, you are more than welcomed to run from source, which makes disabling the XP block trivial.
See:
https://www.mobileread.com/forums/sho...1&postcount=56
https://www.mobileread.com/forums/sho...5&postcount=61
I assume anyone who would know enough to want to try this, would be capable of figuring it out.
No one is interested in making a one-click installer for calibre2.x on WinXP.