

You could look at fire safe boxes for document storage. Those are usually pretty solid. You would want to bag up the drive inside an anti static bag and probably put a couple of those little water absorbing silicone packets in there as well. If access isn’t an issue then maybe some sealant around the seams to keep it more water tight.
Magnetic tape would be better for long term storage as well I think. Those have longer storage stability. I don’t know how long an unplugged hard drive will reliably store information.
Animals could dig it up but probably wouldn’t as it wouldn’t smell like food. Depth wise I’d go for at least a couple feet deep, the traditional 6 is a surprisingly deep hole and temperature gets more consistent the deeper you go (at least with readily available tools, it eventually starts to get hot again).
Please note totally random opinion with very little experience with long term data storage. Thanks for the fun thought experiment, I hope things get better and you don’t need your backup data.
This is a big problem with medicine in general. Medicine is unfortunately very much an old white man’s club, it’s getting better slowly, but all the knowledge and the way it is taught comes from that old white guy standard.
Medical terminology is complex because medicine is complex. There is definitely an element of being part of an exclusive club but there is also communicating lots of information quickly and efficiently.
Frontotemporal dementia describes a specific set of symptoms and if you are medically trained tells you most everything you need to know about what is happening. As opposed to the patient is a bit confused or sees things sometimes which could be many different things.
The language and how diagnoses are communicated are really important, a good medic should tell the patient their diagnosis with the medical words but should explain what those mean in as much detail as the patient wants.
Most patients are able to understand dementia even if the frontotemporal bit doesn’t make sense to them.