As for P+: If you carefully parse @RokuDanny-R's statement about this you will notice he doesnt explicitly state that OS11 would fix the issue:
"We believe we have found a resolution for this issue and expect this to be resolved once OS 11.0 has been fully released."
It doesnt state that OS11 will be the resolution, just that they expect it to be resolved once OS11 has been "fully released" (whatever that means, since we dont know Roku's metric for an OS being "fully released").
It could easily be that Roku found an issue with the P+ app/service, communicated this to P+, and who then decided to wait for the "full release" of OS11 (perhaps on Roku's advice to limit support confusion etc).
Or, it could be that the particular functionality/fix in OS11 that the P+ app needs will only be implemented at a certain (unknown to consumers, but known to Roku) OS11 build level and later.
@RokuDanny-R could clear a lot of this up by stating whether the issue is with OS10.5 and/or the P+ app, and what constitutes OS11 being "fully released".
As for HBO Max and loss of 4K/HDR10/DV/etc, that is impacting several platforms for several weeks now, and needs to be addressed to HBOMax