Originally Posted by ryck
Time Machine is showing a couple of hundred GBs more than it should.
suggests that TM may not be the way to go.

I'd go with an erase/clean install (as you've suggested) combined with migration from the old iMac.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire