I believe the problems with the auto detection option while installing the recent release candidates has to do with the fact, that the installer seems to look for a device with a certain qubes label. However, as I am using
https://www.ventoy.net/en/index.html
To create my boot usb by copying the qubes rc iso, It might be possible that this way the expected label is not found in the usb.
All the best
Kai