I have a 3810X and wanted a spare remote. The 3820X was on sale for Black Friday. When it arrived, I discovered there is a speed difference between the two Roku devices. As such, I replaced my 3810X with a 3820X. During set-up for Apple TV+ (a new subscription), I was not given the QR code option to authenticate with a mobile device. The only option was "Sign In with Remote." I tried Sign In with Remote more than 20 times and each time it failed to authenticate with an error message:
"There were errors signing you in. Wait a moment, then try again"
Many times, I uninstalled the app, cleared the cache, rebooted the Roku, and installed the app again. Each time, it failed in the exact same way.
I went to another 3810X and opened the Apple TV+ app. It immediately gave me a QR code and I registered successfully.
I replaced the 3810X with the old device and opened the Apple TV+ app. It immediately gave me a QR code and I registered successfully.
The software version on both 3810X devices is: 11.5.0 - Build 4235-50
The software version on the new 3820X device is: 11.5.0 - Build 4235-CU