I just remembered that my main iMac still wasn’t being backed up by Backblaze. I had originally figured that pretty much everything is replicated on my second iMac, but for the additional peace of mind, the extra less than $4/month (when paying for 2 years) is peanuts, so now they both are.
The only gotcha is that I have really slow internet in my rural location (12 Mbps down, 1 up), so it’ll take ages to do the initial backup. But I can schedule it to do it at night, and add exclusions to do the most important things first, so it’s all good.