Adding an external HD

A new iMac with locally connected external Time Machine HD.

All my documents are in iCloud Drive (except TM)

is it possible to ALSO use/Store local SSD HD with all my documents?

connect it with thunderbolt usb-c cable for fast data transferring.

I would like to add a local store document place and prefer an SSD instead of iMac’s Fusion Drive.

If so , how ?

Thank you