Backup strategies for two Macs

I’ve been a one Mac guy for a long time and I’ve been using Arq to backup my Mac to Backblaze B2. Now I have an M1 MacBook Air as my daily driver and my Mac mini is now an email and file server that I backup to. Still trying to figure out what makes most sense for backing up to offsite.

I was thinking that I should make Time Machine backups of the MacBook to the Mac mini server and then backup the Time Machine backups several times weekly to B2 via Arq.

Is there any reason that backing up the Time Machine backups is a bad idea? Better to just sync folders (home and Applications) from Macbook over to the server and back that up?

Time Machine will automatically backup to more than one drive. I have separate external SSD drives for an iMac and a Macbook. They both also backup to an external drive connected to the IMac that is the main (~hourly) backup. Whenever the SSD drives are connected TM backs up to them (I keep 2 in my car as off-site backup and 2 at home)
I also regularly use Goodsync to keep my data synced between the two Macs.
They are difficult to buy these days, but I also copy key data, including Apple Mail (zipped) to 50gb Bluray disks every few months. I had a close call with a nearby lightning strike zapping electronics so I don’t rely solely on hard disks and SSD drives.
In theory cloud backups are another alternative but they don’t suit my situation.