I keep getting "Installation of macOS cannot continue. ...download important data etc." warning

I keep getting "Installation of macOS cannot continue. ...download important data etc." warning while trying to install Sequoia on an external SSD. The SSD has been properly formatted. The only other issue is that the iMac's fusion drive became somehow compromised a couple years ago so it has been used as a back up for simple tasks. It's the only thing I can think of that might be causing this, but I am no expert. I was hoping that the SSD install and reassigning the startup disc accordingly would make the machine more useful/reliable. I just can't get the install to happen. Any help anyone can offer would be greatly appreciated.

Thank you in advance.