Hello @paulgrevink
have you tried to disconnect everything from M5StickCPlus2 and fully powering it off by pressing and holding the power button?
Also have you tried to erase flash using M5Burner before installing UIFlow2 firmware?
BTW: I did a test and installed ESPHome basic firmware, then installed UIFlow2.3.8 firmware and then ran M5StickCPlus2_GPIO32_GPIO33_ON_OFF_UiFlow2.2.0 from Project Zone without issue, e.g GPIO32 and GPIO33 toggle just fine between 0 V and 3.3 V.
Note: While ESPHome was installed GPIO32 measured something like 0.2 V.
Thanks
Felix