Thank you for your feedback.
This is normal concept. Device displays Fast/Super Fast Charging when battery level is 0~80%. Anything above that will display "Charging".
If your device behavior is inconsistent with this concept, please submit an error report using the Samsung Members App.
We appreciate your contribution to the Beta Community.
One UI Beta Team
Most start dropping off above 18%.
There's a good video on this. Where they test all the various mfg's fast chargers (even 120w). The wattage draws start high when battery is low, then less and less as the battery charges.
Turn fast charging off, then plug in your charger. Notice the time until full. Then turn fast charging back in, and plug in your charger again, you should see a difference in charging times.