Hi @fstengel I am also running the same setup as you do, lets see if I can help you in any way.
Have you seen this library before? It simulates an encoder with the 3 m5stack buttons. https://github.com/sci-bots/m5-lvgl
If you don’t want to use a simulation of an encoder but want to really simulate button presses then check Hardware Button multiple points (for 1 button this works 100%). I have also made some changes to the encoder library so it would behave as 3 different on screen buttons. (not complete yet). But when I tried the last solution the first time there was a small problem with the lv_indev_set_button_points as you can see. Since then I believe it has been changed. But I still had not the time to check if it works.
Hope it helps.