Buy a book of drills for beginners. Any intro book will do

with your fingers

hannon

Do you just want to play along to pop songs or do you want to read sheet music and actually get to a decent level?
This really helped me with reading sheet music, do some drills every day so you dont forget
https://www.musictheory.net/exercises/note

You can find the Alfreds Basic Adult Piano Course pretty easily which is a good starter

Also if you have a midi keyboard this is good
https://sightreading.training/

Don't feel too bad for using synthesia to learn songs and get a feel of the speed and rhythm of the song but I would still recommend reading sheet music over it