When backing up the 4.4.6 database, the process generates a directory. It's not a ".backup" artefact file...
When we launch the restore commande on 5.2, we have this error :
_org.neo4j.cli.CommandFailedException: --from=path option should contain only backup artefact files (ending with '.backup')
I had the same issue when I was testing the migration from 4.4 to 5.1. I backed up my db in linux and copied the backup file to Mac Desktop. Created a DB in version 5.1 and copied the backup file to data/dumps in 5.1. When I tried to run the restore command I got the same error as you got.
I tried this and it worked:
Step 1: Copied the backup file to data/databases folder in 5.1
Step 2: With 5.1 DB offline, I ran the copy command in the Terminal: bin/neo4j-admin database copy <new db in 5.1> --to-format=standard --force
It ran succefully and created a new db folder in data/databases folder.
Step 3: Started my 5.1 DB, selected 'system' db and ran the query CREATE DATABASE
Step 4: Ran SHOW DATABASES query and it shows the newly created dn with status 'online'.
I haven't tried this in the production db in linux. We will soon be trying this with our production db.