Can I backup to a Spinning HD from internal SSD boot drive
 

I*m running Catalina on a Late 2915 imac. Internal SSD is 1TB APFS and want to back up to an external 1TB spinning HD. It*s formatted to APFS. Do you recommend this format or would I be better off with HFS+.

I read about negative issues with APFS and spinning drives

Thanks.
Matt

Catalina requires APFS. That's the only option. But I would generally suggest using an external SSD - they're about $150 for 1TB.