Try a different HDMI port? Different cable?Audit13, it is an Onkyo TX-NR646, and the ATV is connected directly to it via an HDMI 2.2 cable. The Onkyo is running the latest OS.
tvOS 14 has been a nightmare for a good many home theater enthusiasts (believe me, I've heard from them!). However, going direct to AVR has usually been the one set-up which has worked fine for most users.
Another option is to sign up for the tvOS beta program and see if the upcoming 14.5 update helps. Folks around here are saying this update fixes some of their issues.