Often, it’s not really the “old games” but the “not the marketed shit”. One of my favourite gems is Outward. It looks and feels a bit clunky, but you breathe love and passion for making games on every corner.
Definitely try solo stuff with plugy. I installed D2 for a nice bnet session of baalruns but bnet was a bit riddled fuckhole. I tried plugy before uninstalling and it got me hooked on solo play for 3 more years.
I have stopped giving even the slightest fuck about Ubisoft games. There are way more games than I have time. It’s just another filter for what to play next.
Usually, I find ports of PC Games best. I don’t know if they are suited for 9 year olds, but broken sword, baba is you or papers please are really good on mobile devices. Point and click in general is a very portable genre for mobiles.