I read on the internet that some have used the mysql database to make simple 2D games such as “tic tac toe” on android mobile devices. I wanted your opinion on it. Alternatively, what could I use to make multiplayer games on mobile? how to put them on a server?
You don’t need a database for tic tac toe, that’s overkill.
Just use UNET: https://docs.unity3d.com/Manual/UNet.html