I know you can have two Time Machine drives on the go for the same computer. I have two Time Machine drives and alternate them so they are in effect duplicates.
A topical topic: Howard Oakley wrote this just last month. It might help.
He has written much on the subject of Time Machine back-ups and the summary is that it is complicated. TM has changed greatly over the years, not least because of APFS, so be wary of too old and too new info.
Douglas Cheney 