Not so much about your property surveying, but given that you brought up the subject of magnetic vs. true north, there are some things related to the shifts in magnetic north that are probably worth bringing up here...
Magnetic north has started shifting pretty rapidly in the last 20 years - it's not as stable as it used to be. Historically it's been moving away from Canada and toward Siberia at about 5 miles per year, but for the last 20ish it's been moving at around 30 per year. Presently it's about 1,300 miles off where it was two hundred years ago, and is still moving away. It's a pretty good idea to know how to find true north day or night, and keep up to date on being able to adjust for declination in your area.
Something that may be related that can also affect our backcountry navigation, is that there's some pretty good evidence that our planet's magnetosphere, which blocks out a lot of the electromagnetic radiation coming out of the sun, is weakening - it's lost about 10% of its strength in the last century or so, and it's increased that rate of weakening for the last 15. About half of this loss in strength has occurred during this recent period. Weaker magnetosphere means more electromagnetic energy penetrating deeper toward the planet's surface, causing more damage to satellites and possibly other electronic equipment than it could have just 20 years ago. Elon Musk lost a bunch of satellites a few months back from a solar storm that shouldn't have caused that much damage, likely because of the differences in magnetosphere strength between what existed and what was engineered for.
Add to this that the sun's on an upswing in one or more of its cycles, and it's increasingly pumping out solar storms and coronal mass ejections - a couple of weeks back it ripped out a solar flare at least as big as the Carrington Event one in the 1800s that fried the world's infant telegraph systems, to the point where it was lighting some of it on fire. We got lucky in that this recent one was pointing almost exactly opposite of Earth, but had it hit us there's a good chance the sun-facing side of the planet would have had its electrical grid go down, along with most of the planet's orbiting satellites.
While I rely on GPS and OnX in the back country, I also try to find the best paper maps I can of an area as backup, but it's increasingly difficult to find them. Anyone have any good sources?