fenix 6 s pro not counting steps

That looks either like a hardware failure or a corrupted firmware for sensors (SNS / Sensor Hub). First of all, go to the menu on the watch » System » About and scroll down to the pages with all the firmware components like GPS, CIQ, ... and especially note the SNS version. If some of the components show version 0.0, then it usually means that the firmware could not be installed properly. Reinstalling it can sometimes help, but usually you have to find an older version of the SNS (Sensor Hub) firmware, install it together with the corresponding main firmware. If it helps restoring the functionality, you can then try updating to the current version again. You can find information about the manual downgrading in the Wiki on the Beta Program forum.

You can also enter the diagnostic menu on the watch - shut down the watch, then start it while holding the Down button (bottom left). You can scroll through the diagnostic screens with the Back button (bottom right). One of the screens contains the SNS data with the accelerator and gyro values for all three axes. You should see great variations when you tap on the watch. If not, then the sensor is possibly dead.