Well I suppose there're lots of people who never ran into any problems. I've been using Ubuntu and Mint mainly, and usually that works fine for me too (with most laptops & desktops I've had). In one case though (maybe 3 years ago), on fairly new hardware IIRC, I've had to test various kernel versions, until I found one that was compatible with the graphics stuff on the laptop. And then take care to not accidentally auto-upgrade to another kernel version. In another case, networking in Ubuntu didn't work after installation. I installed another distro instead and then everything (incl networking) worked fine directly. Finding printer drivers that doesn't just print random garbage characters, is usually super frustrating (I think), largely because the printer company webites' UX is terrible.

I think one is safer, if one use a bit older hardware (laptops and printers), because then the Linux people have had time to look into bug reports and incompatibility problems and fix them?

Nowadays when buying a new laptop, I always websearch for the laptop name + "Linux problems" or something like that, to see what bugs & incompatibilities other people have reported already. And then maybe I decide to avoid that laptop. But ... I wouldn't expect my parents or most other people to do this. Instead they'll buy a "random" laptop with new "unknown" hardware, and then there'll be a 20% ? risk that networking or graphics won't work for them? And I think they'll need help to get the printer working. ... And with all that in mind I feel I need to slightly warn them about Linux.