I want to mean for ‘LV_BTN_STATE_TGL_REL and LV_BTN_STATE_TGL_PR’.

Do you know the examples for LV_BTN_STATE_TGL_REL and` LV_BTN_STATE_TGL_PR '?

They indicate “release” and “press” events respectively (LV_BTN_STATE_TGL_RELease and LV_BTN_STATE_TGL_PRess). I agree the documentation is ambiguous on the matter even if it might look obvious.
They are used to specify input events (button press and release).

In addition to what @Mattia_Maldini pointed out the TGL in the name indicates that the button is also in toggled state (independently of being pressed or released).

The example in docs could help to clarify it further.