That just uses normal fast charging to get to 80%, then stops the charge and finally resumes charging about an hour or two before the planned “charged by” time. No slowing down.
Oh, and it also has (or had on Android 13) a cool bug where it just stops charging if it fails to reach 80% by the time it wants to resume charging (for example if you put the phone on a slow charger late at night - that’s how I woke up with 60% battery after 4 hour sleep).
So I just gave up on the idea of using a slow charger to better preserve the battery because the phone clearly wasn’t expected to be used that way.