Final Update:
As of yesterday, HBOMax was STILL not working. Get the HBOMax purple splash screen, then rotating dots at the bottom, that rotate forever (OK, just hours and hours, I actually left it going overnight once).
Roku here was no help. HBO says it's a Roku issue.
Apple had a $25 credit discount and my Amex card had extra miles at Apple, so I bought an AppleTV. Installed it yesterday.
All is good in my streaming world now. All my streaming apps work well (HBOMax, Showtime, Hulu, Amazon, Netflix, Disney+) and as a bonus I don't see any advertisements like Roku blasts you with on the Home screen, etc.
So yeah, a short term pain to buy the more expensive AppleTV, but for me totally worth it.