Yes, entire storry with HQ Camer asupport on Stellarmate is very confusing if not missleding.
I to bought Stellarmate in belive that it support HQ Camera. Since then struggling with it and my HQ Camera with no luck. But there is hope at the end of the tunnel.
There are two versions os Stellarmate, 32 bit (buster, no longer supported) and 64bit (bullseye, supported).
32 bit version kinda supported HQ Camera witn indi-rpicam driver, but that driver was very buggy and long exposures didn't worked at all. See this: github.com/indilib/indi-3rdparty/issues/271