https://www.bbc.com/news/technology-57443598
TL;DR Windows 10, which was going to be the last version of Windows, will be killed off as of October 2025.
I think it's time for me to explore Linux. I have an old Dell desktop computer I can use as a test bed. What are the current flavors of Linux that are the most popular and easiest to work with (in terms of printer support, etc.)? Which look the most Windows-like (preferably like Windows XP, or maybe Windows 7)?
Mint Linux is what you want.
"Cinnamon Edition", 64 bit, on any remotely capable modern hardware.
it comes up looking a lot like recent not-8 versions of Windows. Launch/task bar across the bottom, start button thingee in the lower left corner, indicator applerts in the lower right. Control panel like Settings area to configure all the usual stuff. Windows Store equivalent for easily adding apps.
Going to that is really no more jarring (in terms of getting used to stuff) than going to Win 10 from Win 7. IMHO&YMMV.
Printer support is pretty good, but research purchases first.
Can I start playing with them by running them from a DVD or thumb drive?
Yes
Microsoft has a track record of alternating really horrible versions of Windoze with fairly tolerable versions. Windows 10 hasn't been horrible, so anything that replaces it is virtually guaranteed to be bad. Aside from which, Microsoft still hasn't learned, 'If it ain't broke, don't fix it."
https://www.windowscentral.com/windows-10x
With Windows 10 MS went to a semi-annual major release upgrade cycle, which is just like what Ubuntu has been doing for ages. (And, just like Ubuntu, there's a Long Term Release version that tracks an older release, but keeps current with security. Win 10 Enterprise LTR currently is 1809, I think.) The nifty thing about this is, you can get pretty close to current in one fell swoop by using the current installer. You don't have to nurse, like, 5 years of updates, servicing stack upgrades, etc.