Trying to reinstall Sequoia on my iMac Retina 4K late 2015

Had to start over on this iMac and so it now is running Monterey. It was doing fine with OCLP and Sequoia but I had a glitch and had to wipe the machine and start over.

This morning I built the installer as I have done several times on this machine and others but for some reason, when I do the final reboot to install Sequoia, I hold down command when I see the Apple logo, and then I end up back at the Monterey log in screen.

If I try to run the installer from the USB drive, I get an error message saying ti isn't supported.

Can anyone help me? Thanks.