The blog ChargerLab claims to have found that some wireless chargers are being restricted to 5 watts (W) of power while iPhones are placed on them with the new iOS update, whereas the same devices could deliver 7.5W under the older software version. However, this apparently does not affect those brands that are sold in the Cupertino giant's stores.
https://www.notebookcheck.net/Researchers-claim-Apple-restricts-wireless-charger-speeds-in-iOS-13-1.436966.0.html