Any thing of any importance at all is on my EndeavourOS LAN file server, NAS, or whatever you want to call it. My home directory is just about bare. I use rsync to backup the main NAS SSD to a secondary USB backup SSD in an enclosure. The Secondary SSD is only hooked up to the NAS during an actual Backup session. That way the backup SSD is not normally powered up, it is basically in storage. About twice a year I swap the Main SSD with the Backup SSD and spread the usage between them.
Here comes the on topic part. Here is my latest scheme for off site storage. I got a name brand M.2 SSD 2280 (not NVME), then bought a M.2 to USB external enclosure I’m not necessarily pushing this particular name brand, but something like it.
I use rsync to make a copy of my NAS SSD and then take this to my daughter’s house and she stores it in her safe. Or one could put it in a safety deposit box in your bank. Now in case of an extreme disaster such as the house burning down, I still have a relatively recent copy of my data. I use rsync because when I later update the off site SSD it only has to deal with what has changed.
My daughter is about an hour’s drive away. When I get some extra discretionary cash, I am seriously thinking about buying another one of these set ups. Then when I am going to her house I could make a current backup and then swap them out, then bring the other one back for next time. Right now, I go to her house for a visit, bring home the SSD, then make a backup just before the next visit and take that to her. In the mean time, my off site storage is no longer off site until I return it. Sort of defeats the purpose.
As to reliability, IMHO M.2 SSD are as reliable as anything available on the consumer market today. If you want better then maybe Enterprise SSDs would be appropriate, but bring your wallet!
This setup is larger than a USB thumb drive, but smaller than a 2.5 inch SSD or Hard Drive in an external enclosure.