Some clarifications :
The 3 2 1 rule applies only for the data. Not the backup, in my case I have the real/live data, then a daily snapshot in the same volume /pool and a external off-site backup
For the databases you got misleading information, you can copy the files as they are BUT you need to be sure that the database is not running (you could copy the data and n the middle of a transaction leading to some future problems) AND when you restore it, you need to restore to the exact same database version.
Using the export functionality you ensure that the data is not corrupted (the database ensure the correctness of the data) and the possibility to restore to another database version.
My suggestion, use borgbackup or any other backup system with de duplication, stop the docker to ensure no corruptions and save everything. Having a downtime of a minute every day is usually not a deal breaker for home users
Dealing with a Ds-lite connection for a fiber optic provider in latest opnsense.
It is excruciating how difficult is to run it reliable