I’m not much of a car guy so I googled how long it takes to let air out of car tires. I guess it only takes a few minutes?
It takes about 30 seconds to significantly deflate a standard 28-inch bike-tyre by pushing in the pin on a
Schrader valve-core, so sure, an SUV-tyre would likely take a good couple of minutes.
But if the attacker is carrying a valve-core extractor-tool like this one

...it would take them only seconds to obtain a near-guarantee of complete deflation for all 4 tyres. It's not even necessary to unscrew the valve-cores all the way: a couple of turns would be enough to break the outer O-ring's seal against the inside of the valve-stem, and the the pressure differential will do the rest. Even if the victim returned to their vehicle while the valves are still leaking, the source of the hissing might not be immediately apparent.
If the victim also owns a core-extractor and a tyre-pump, the deflations would be very simple to repair (though likely inconvenient). But if they don't, then they'll need to call out roadside assistance (inconvenient
and expensive).
The technique used by the activists is to put something like a lentil under the cap, so when the cap is screwed on to the valve it pushes in the nipple and lets air out slowly.
Yeah, that would work too. But creating slow leaks is arguably more dangerous: if the victim can't hear the hissing, they may drive away while their tyres are still deflating, increasing the risk of them having (or causing) an accident.
As I might've said before, I have little to no sympathy for the urban-tractor drivers — the
only possible justification for owning an SUV (IMHO) is that one's livelihood requires frequent driving on unsealed tracks (e.g. farming, forestry, etc.) — but I would draw a definite line at deliberately endangering them.