Mobile phone connected in WIFI, client list in admin panel is detected as offline device.
I just tried mine, firmware 3.203 and iphone 11. It appear as online.
Can you check your phone’s wifi connection to see if you have used private address? Sometimes I use private address and my phone will be identified as a different phone, so may appear as offline. But this may not be your case.
I do think there may be bug and reported to developers