This is not an issue with the Roku Channel. It's related to the 12.5.0 Software Update. I had a spare Steaming stick that was on OS version 11.0.0 and screen mirroring worked fine. Then it auto updated to 12.5.0 and mirroring failed. Below is a breakdown of ,y devices and what I have tried.
So far I have...
* Verified AirPlay is turned on
* TV Fast Start (for my 2 Roku TVs) is on
* Screen Mode set to Prompt
* Network Resert
* System Reset
* Factory reset (on a Roku Ultra)
All of my Roku Devices have been automatically updated to 12.5.0. I had a Streaming stick at 11.0 which worked, but then it updated and it now no longer works. Below will be the information you requested for each device...
TCL Roku TV (LR Roku TV)
Model: 50S455
Serial # x01200EWRPDJ
Device ID S0JR2DWRPDJ
Software/OS 12.5.0 build 4176-CG
Tracker ID DJ-515-762
TCL Roku TV (BR Roku TV)
Model: 32S327
Serial # YK00CC721737
Device ID JDA87C721737
Software/OS 12.5.0 build 417648
Tracker ID 37-515-767
Roku Ultra
Model: 4660X - Roku Ultra
Serial # YJ004F871983
Device ID CK3934871983
Software/OS 12.5.0 build 4178-46
Tracker ID 83-515-771
Roku Streaming Stick+
Model: 3810X - Roku Streaming Stick+
Serial # YH00673692819
Device ID 213157692819
Software/OS 12.5.0 build 4178-50
Tracker ID 19-515-842