Thanks Jurgen to join my request to debug A7S driver.
To add some details, I would say that M mode is possible but when switching to non Bulb mode, capturing an image will result on a faulty situation. The first image will be ok but the second one is still the first, the third one is the second and so on. This situation avoid using autofocus and astrometry since Kstar is not analyzing the good image.
In the last version of indi and gphoto driver, I notice that in fact when using "RAW" mode the capture download "RAW + JPG". This situation leads to use RAW for the first shoot and JPG for the second, introducing a gap between gphoto driver and Kstar.
I open 2 bugs in github here and here

Like Jurgen I not skilled to debug myself the driver code, but I can contribute doing test sessions.