is it possible to Use Precision Finding of air tags to find a house door?

I do this and it is easily accurate enough to not just find the door but in my case the door handle. I use an air tag holder intended for dog collars that I wasn't happy with, it just has a big loop you put through itself like some lanyards and I hang it from the inside handle. All you need to do is get within range which can be a little hit or miss as you walk by, I find I have more success if I'm walking a couple feet away from the building line it seems to give the phone a better signal from the airtag.

I haven't used AirTags. I understand they use batteries, so as long as your battery doesn't die, it should work.

Many outdoor navigation apps let you place a beacon, which isn't a perfect solution due to commercial GPS imprecision. It would get you close to where you might want to go, but might be 5 or 10 meters off on any given day.

You might be able to view the tag on a map, but precision finding only works from around thirty feet away. So no, you won't be able to get directions, as such, just a general bearing/distance.

When out of the range of the AirTag, you could use what 3 words. Find the What 3 words grid name for your door/entrance and save it – you can then use this for navigation plus I believe Uber accepts a what 3 words address for delivery/collection points so no more dropping off at the wrong place.

I find reliable connection closer to five to ten feet, walls can interfere wit this. Think of it as more like bluetooth. Once connected the accuracy is such that it can not only guide you to the jacket containning the airtag, but also the pocket the airtag is in.

Battery expectancy for an airtag is over a year depending on how heavily it's used and the app warns you well in advance when the battery needs replacing. They're standard CR2032 cells so they're pretty easy to obtain.

Sorry, what are you talking about?

What three words is an app which replaces numeric coordinates with a name created using three words from a long list, the world being divided into squares roughly ten feet across. It's meant to be a more understandable way to convey location information and doesn't rely on addresses, it can be useful for finding the exact location especially for larger buildings or campuses where you might need to specify the location of an entrance. It's also been used in some cases to rescue people who get in trouble during outdoor activities.