Using two different drives with Time Machine I have two drives that I want to utilize with Time Machine.
Every week, one is rotated offsite.

Week 1 - Drive A is utilized for Time Machine.
Week 2 - Drive B is introduce, and utilized for Time Machine.

Rotation:

Week 3 - Drive A is used, Drive B is offsite
Week 4 - Drive A is offsite, Drive B is used

So at most, one week of work is at risk.
When I introduce Drive B at week 2. It has no backups. Time Machine present option, &quot;Do you want to use both?&quot;
Just select &quot;Use Both&quot;. Thats is all that is required. Both Drive A and Drive B will have full backup, one week apart?
You can have Time Machine backup to several drives, it will rotate among all configured and mounted drives. Two caveats

if you disconnect a backup drive, Time Machine will alert you the next time it‘s up for backup
If you disconnect a backup drive for a week it‘s next backup most likely requires a full scan of the source drive

It might be better to keep the two drives connected all the time and do alternating disk image backups to two other drives (and store those offsite).