I have the same issues - have done all the fixes as well. My issue began when I upgraded from wifi 5 to wifi 6 router (AX55). Have done all the unplugging, re cycling, etc etc etc. My ROKU TV TCL is AX0000 which supports airplay. Clearly there is some king of bug due to the new tech of a wifi 6 router that ROKU has not fixed for quite some time.
After upgrade wit wifi 6 router I wanted to mirror my iPhone screen to Roku. I have tried the following steps in an attempt to fix the issue:
Checked router configs and rebooted
[x] Rebooted Roku.
[x] Rebooted iPhone
[x] Verified that both devices are on the same Wi-Fi network
[x] Verified that Roku can stream YouTube contents
[x] Verified that Airplay is enabled on Roku
[x] Disabled IPv6