The best backup is another copy of what you already have so I'd say another Mini 5 Pro. All your accessories are interchangeable and if you crash one then that becomes a parts bin for the other. If you really want something different (or cheaper)...
This “experiment” ended-up taking 3+ years, condensed into 3 1/2 minutes (Arizona has mostly cloudless skies). Three drones, A2s, A3s, M3. Predicting whether a sky will blossom is nearly impossible. All the prediction Apps are as hit and miss...
If it ain't broke, why worry about fixin' it? LOL!
Keep flying it like you stole it, until you can't, which may or may not happen.
If it’s already been a few months, it may be too old to be affected by the current periodic logouts on newer drones.
I don't think private ownership of these cars is in the cards unless of course they are all hooked up to some sort of Universal A.I. Transportation grid.
But if they can do that, Why not commercial airliners? NOW as with everything else, we will...