My 75 year old father in law have been running vanilla gnome for the last 5 years. Turned out to be less confusing than Windows and less ways to mess up the computer. Only support I had last year was when the printer queue was paused for som reason. But I also helped a relative with the same thing on Windows 11 a few weeks ago, so that seems to not be a Linux issue.

So, Gnome is pretty much suitable for your grandma.