I'm not sure but i think i heard there was a solution for some rooted phones to stop charging at a specific battery level (magisk Module maybe?). Similar to al dente on a mac.
Maybe you could look into that
"To protect your battery health and help extend its lifespan, your phone automatically limits charging to about 70%-80% under certain conditions, such as:
Continuous charging for more than a few hours under high temperatures.
Continuous charging for more than several days."
Per the way that feature is supposed to work, leaving it plugged in all the time would stop charging at a certain point in an effort to prevent battery degradation and thermal runaway.