Thank you for reporting. Yes, what you described is exactly the problem.
@TSD17
Ser# X01000DD347PKEL5
Model 4801RW ROKU ULTRA
Device ID. SODD347PKRK5
Software 14.0.4
Channel build 15.0. 12221-DE
TRACKER ID K5-467-329
Still can not sign in to Apple tv app on Roku Ultra
