I know there is no support for tvOS betas, but I thought I would mention it seems the non-DVR Channels ATV app is working on tvOS 15b2 on ATV 4Kg2
Not sure which of the following fixed the issue, since they were all released on the same day:
- tvOS 15b2
- Channels 4.5.7
- Connect 4K 20210624 firmware
- Rebooting Connect 4K after all of the above