Just tried again this morning with 6.2.3.4 - h265, HDR/HDR10+, attempt 4K (knowing I won't get 4K), Atmos audio (English), English subs. US server from within US, no VPN. Same result.
6.2.3.4 was a downloaded-installer upgrade from 6.2.3.3, which was a downloaded-installer upgrade from 6.2.2.2, etc, going back several versions. No online upgrades. The only other service I'm having problems with is Netflix (not getting 1080p), but I feel mostly confident that issue is not related to this issue (haven't looked into that yet).
Fresh log attached.