I never tested Android 8.1. With crDroid 6.10 (Android Q) charging the battery with the Tuned Kernel works perfectly. When the battery is fully charged, the charging process stops and the control LED goes out after a while. No warming can be detected.
I've been using the SmartPack Kernel Manager for a long time. With this app, the max. frequency can be set in the long term without any problems. The current version is available on Google Play.