This year, so far, I've moved two older family members over from windows 10 onto Linux. I opted for an ubuntu based distro as I'm familiar enough to troubleshoot it, even remotely.
The first was a laptop, about 10 years old; windows was unusably slow. Luckily, the transition was smooth, Linux Mint took first attempt and no issues were had, everything worked out of the box except swipe scrolling - a quick tutorial sorted that out (terminal intervention was needed). 4 hours total setup (including a pile of desktop shortcuts), dual boot just in case she had issues.
The second was an older machine, a desktop, Frankensteined out of old parts (oldest being the motherboard at 15 years old). It ran windows 10 without a single hitch or slowdown.
2 days to get it "running", I had to repair grub to get the damn thing to boot after an install finally took. In the end I had to go with lubuntu with a manual cinnamon install because I hit my 4th mint install attempt and got a strong case of the"fuck thats". At the end I have a machine that has ghost headphones flickering into existence giving choppy sound that is pretty unusable. There is also horrific graphical glitches when booting (harmless, but I crapped a brick when I first saw it) - though I suspect this is just the fact there is an elderly Nvidia card in there.
A lot of time spent in terminal was unable to even identify what was happening - a first for me! My money is on a bios update, but yeah, not fun on old boards.
All in all, two very different experiences. It's not a warning against Linux (make the change now while the support is there!), just a warning that the road isn't always smooth. The bumps can come in odd places - you'd think the laptop would be the tricky one but nope, desktop rig was the worst.
Good luck out there with the change folks!
Local government's have had such opportunities for decades, the evidence suggests that this doesn't work overly well.