I don't know about high quality but I'm also part of the group who are disappointed by how mobile games these days are simply Pay 2 Win or ads filled.

A few games I used to play during lockdown (no P2W and zero to very little ads):

1. Adventure Quest 3D

2. Critical Ops: Multiplayer FPS

3. Payback 2 - The Battle Sandbox (turn off internet to disable ads)

(I know you didn't ask for games but sources to find such games, but still sharing so as it may help someone :) )

Some thoughts:

1. Indie developer games or paid games often have a good quality

2. You might try gaming console emulators to play the console games on your phone (the old ones) but yea - it involves legal issues