trying to upgrade from High Sierra to Monterey and receive error that the hard drive is being encrypted and install fails

Hi,

I haven't run into this before, but based on what you posted, someone turned on encryption and upgrading is not possible until that encryption is completed. I would let it go overnight and try again tomorrow.

Filevault state, open Terminal & paste these in & press enter…

    fdesetup status

    diskutil cs list | grep 'Conversion Progress'