Ok. Didn’t take me long to figure it out. Need to launch the PS4 version. Go to the load screen and there’s an option to upload saves to PS5.
Then go to screen where you choose modes and there’s a titchy tiny cloud icon at the bottom (left, but I don’t know if that’s because it’s under normal mode for me). Then you download your saves and you’re good to go.
It’s loads unbelievably fast, looks AMAZING, and I can hear it over the noise of my PlayStation for the time!
\o/
Tagging @Jogort