Thank you for the useful reply.This app works by modifying the value of the charge control file. Mostly located in sys/class/power_supply/battery. You have to manually check which control file works in case its even possible for OP9 devices. If nothing works then maybe you need to flash a custom kernel like for ex. Kirisakura kernel for OP7? IIRC.
You can also try ACC module but it didn't work reliably for me. Now I have setup Tasker to control charging in my Xiaomi devices. Plus it can also stop charging if battery temp. gets too high unlike BCL.
Can you share the Tasker script ?