Hi After updating linux-image-686 with the latest update (5.17.0-2-686) , finally my machine successfully boots. The problem should be solved also for other people affected by this bug.
P.S. : For other people interested , starting from linux-5.18-rc5-rt4 and beyond ( latest I've built is linux-5.18-rc6-rt7) my system is shutting down correctly in both power off and restart modes. And I suppose it should be the same for other 686 class users that are running a RT kernel :)
