As someone who's built commercial RF test enclosures on the scale of a house, "trivial" is not a word I would use.

Putting shielding foil in the walls is quite straightforward. Putting mesh in the windows and doors, or using solid metal doors, too.

Connecting the moving parts of the windows and doors, to the walls, in a continuous way that maintains a useful amount of RF shielding, is absolutely devilish.

Basically you end up with conductive doorjambs, which can't be aluminum because it makes a thin oxide layer over itself which is not conductive. They can't be stainless steel, which does the same. They can't be plain steel, because it rusts, or copper, because it tarnishes. You're left with brass, gold, or silver as your options. (Or, try aluminum and just use massive contact areas, so the joint functions as a capacitor across the oxide layer, which is effectively a conductor at RF even if not at DC.)

The corners of everything are murder. The soft flexible bits of "weatherstripping" are most subject to damage, and everyone who opens the door has to be trained on what parts not to touch, or how to re-fluff and repair whatever happens. You can make a notched overlapping sort of structure, but you end up with a 4-foot-wide door that opens on an articulated hinge to reveal a 3-foot-wide opening, or a bank-vault-style giant lever that operates a mechanism to engage the door seals. Or a fairly normal looking door with substandard performance and you put a few of 'em in series in an "airlock" sort of structure.

Doorjambs are a special challenge, since you want the jamb to be fairly low so you don't trip on it, and so you can roll equipment in and out. But that means all the sealing has to be part of the door, and you really want that vault-style compression mechanism. Or, you have a small high-jamb door that humans can step over, and a separate large equipment opening that you only open once in a while and just re-seal the perimeter with copper tape every time you close it.

Getting wires in and out is also a chore, though there are products for this, they're expensive. Without a proper passthrough, every wire that penetrates the envelope is basically an antenna that re-radiates signal on the other side. A single fire-alarm wire is enough to pass quite a lot of wifi signal! And good luck getting the fire AHJ to accept your notion of shoving a bunch of additional components on their wire to filter this RF stuff that they have no idea about. Got a safety cert for that?

AC likewise needs filtering, and the more power you're moving, the beefier the filters are. And the bigger they are in a physical-dimension sense, the harder it is to get them to perform at high (GHz-plus) frequencies, because the individual geometric features are resonant. You can't throw money at this problem, it's physics, so you just have to get clever. One approach is to put the breaker panel outside the enclosure and pass individual circuits through, since each individual one has lower current requirements and the filters are smaller.

Mind you, this is not a theoretical or absurdist "we want to block everything" exercise. Until the guy with the spectrum analyzer showed up, our quick test during assembly was just firing up a phone and seeing if we could link to the wifi AP on the other side of the enclosure wall, exactly the real-world scenario you propose. Every measure I've described here was necessary, and if we screwed up a single detail, we'd get wifi signal back.

It can be done. It's neither cheap nor easy. It helps if you have good test equipment and a lot of intuition for how RF behaves. And a massive, massive box of copper tape.