Saeco Vienna grinds beans but doesn't stop grinding or proceed to brew

There is a microswitch that sends a signal to the circuit board which starts the doser solenoid and the brewing cycle. Could just require dismantling and cleaning or new switch. Worst case new circuit board. Unlikely it is the solenoid Most likely needs cleaning.

Google for "Saeco Vienna Testmode". This will help determining the issue, e.g. this video. I see two possibilities: the microswitch of the grind chamber, as mentioned above, hopefully a cleaning ist sufficient, maybe a replacement of the switch. You will find the chamber following the outlet of the ginder.

Or worse: a faulty PCB, in this case a replacement is an option. Much cheaper is the replacement of some parts on the PCB, there are repairkits. Good luck!