How did your project go/end?
I'm currently trying to do exatly the same thing as you on a BigTreeTech Mini12864. (I think very similar to what hardware you have) I want to control it from an Arduino UNO, but without much success, and was just wondering how you figured things out.
I would really appreciate an update, thank you.
Start by getting the encoder to work, there is a lot on the internet about this. Then have it let you knows its position with a max position. Then determine what to do when going past the max or min points. After this you have a count, just correlate that to your menu.
So I actually ended up going with an esp. Then just hooked a nice screen and rotary up to that. I used lvgl for the graphics. I think Lilygo actually sells some boards that do everything you'd want and would probably be better than trying to bend a big tree board to your will.