Comment by 51Cards
I taught my now 83 year old mother to use an Android phone 10+ years ago and now I use Nova Launcher to do my best to emulate the experience she's used to every time there is an OS update. She does pretty well, but recently Google changed the default Phone app and she hates it. It's tricky keeping the experience stable once they have learned it. There are also several "senior" launchers meant to simply the UI but all of them have been a little too restrictive.
Might be worth it to try Fossify Phone as an alternative phone app. If anything, it's less likely to change overnight.