Remote is somewhere like Nullarbor, which is 183 miles from Ceduna (population < 6000). It's over 1000km to Adelaide (population 1.3m) or 1600km to Perth (population 1.9m).
My sister lived in Wingellina[1][2], Western Australia which was a 6 hour drive on unpaved, 4WD required track from Alice Springs. That's close to one of the most difficult, isolated places to get to in Australia, but even there isn't a week on Camels. Maybe going further west into the Great Sandy Desert might get close (although you get close to small townships in WA if you go too far).
The Empty Quarter has low population density but is smaller than isolated areas in Australia.
There are probably places in Siberia and Canada that are fairly isolated too.
I agree that there are more isolated islands. The Pitcairn Islands is the most obvious case.
[1] https://maps.app.goo.gl/Q2wL9KCa9aXht3YS9
[2] https://en.wikipedia.org/wiki/Wingellina,_Western_Australia
But a good example of remote is Nulato, Alaska.
Point is, yes USA is huge (let alone Australia) and skews our sense of distance, but 100 miles is not as trivial distance as we sometimes instinctively feel :-)
I can leave Denver and be DEEP into Wyoming in 2 hours, or it can take 90 minutes to go 60 miles in Rural Virginia (80mph speed limit vs 60 mph speed limit)
If your vehicle breaks down, how screwed are you?
Do you have cell coverage to call for help?
Will anyone be passing by to flag down, any time soon?
How far away is the nearest LEO agency, fire department, ambulance?
How far away is the nearest place for water, food, etc?
Some people just love not having people around, in which case you really want low average weekly population density within say 5-10km (out of easy visibility and hearing).
Some people are concerned about civilization collapse or civil war or... something (ie, the prepper type). In that case you can imagine population dispersing away from (and possibly towards) major population centers over a period of months, and you want true isolation.
I know you didn’t mean Low Earth Orbit agency, but the thought is funny.
If you’re not more than 1000+ km from the nearest satellite, you’re not in a remote area!