Hi Martin. I have have no problems with the QHY294M as long as I use a good quality powered USB3 hub - I use the Anker 12V powered hub (see my earlier post). Also make sure you are using an adequate power supply for the PI. A PI4 needs a minimum of 3A@ 5.1V when attaching power hungry USB kit.
The only issue I had originally was that the fxload program in the package I installed was out of date and did not support the camera.
I updated it from the QHY SDK (32bit arm for Astroberry). To check fxload use fxload -V:
[EKOS]$ fxload -V
Jul 16 2021 (development)
This is a recent one. If it is years out of date then update it.
QHY cameras all seem to require more power via usb than ZWO equivalent ones.