FP5 here as well, but currently running iodéOS. Rooted with Magisk as usual.
I installed acc these days, but it does not stop the charging at the set pause_capacity.
(Set it via the AccA-App, but I also see it in the settings acc -s … current test value is 95%)
I use the Magisk Module. First used the latest release from github (October 16th 2023). Then I installed one posted in the TG channel ( acc_v2024.1.19-dev_202401190_2033.zip ) and I got the same behavior.
I discovered that there daemon crashes, when the pause_capacity (upper % limit to charging) is reached. I also got another dev build there but no change.
Notification states (when the pause_capacity limit is reached):
> Shell
> 🔋ACC
> "⚠️Daemon stopped with exit code 7!"
→ Exit code 7 means: “Failed to disable charging” (can be seen in acc -h)
So I had some exchange in the TG channel and the final diagnosis (from VR-25 - the acc dev) was:
VR25, [23.01.24 16:33]
As per your kernel’s charge_control_limit_max value, the max is 4. You can go from 0-4. However, tests suggest that max value only limits current to about 500 mA, instead of dropping it to zero (as with other devices). There’s something wrong there (in the kernel). Your test with a max of 9 also did not do what we expect. So, you’re out of luck, for now.See if you can find a custom kernel.
I did not really inform myself about idle mode tbh. I wanted simply set a charge limit for now.
First dump question: Is the Kernel of the different available OS the same? Or do the Custom ROMs also modifiy the Kernel? 
(I’m on iodéOS, @Quigley is on /e/OS right?)
@Quigley : What is the result for you when you run acc -t in a terminal (root) on the phone?
→ acc -t
Do all the “switch charging off”-attempts (here 8 test will run) fail for you as well? (the number in brackets does not go over 4 for you as well? switch: off (4) )