The best spray foam jobs (and the ones I see Mike Holmes do) there is no interior gyproc panels - there are just open joists or studs, you can see the abck of the exterior wall (or floor of the room above the garage…)
Some houses I ahve seen under construction - the foam expands just a bit more than the studs, and then is sawn off level with them so you have a uniform seal.
The health problems that gave spray foam a bad name (at least, in Canada) came from Urea formaldehyde foam. In the 80’s it was the latest and greatest tech; unfortunately,it was sometimes applied incorrectly by fly-by-night operators. Improperly mixed, it gave off formaldehyde, making for an unhealthy house (but you sure save on funeral costs!).
It got so bad in Canada that CMHC (like Fanny Mae/Freddie Mac but well managed) refused to insure mortgages for houses with that foam. Unfortunate owners had to rip off their interior walls to carve the stuff out, at huge expense.
the technique was to drill one or two holes between each stud (from the inside, or more commonly and simpler, outside). foam was injected and you hoped it filled every nook and cranny. Compared to hosues insulated before the 70’s it was regardless an imporvement. How those holes were covered over was another story; if done badly, it looked like a row of polka dots on the stucco. Other horror stories involved overfilling, causing walls bulges and cracking as the foam expanded. (Which is why bare studs are the best way to go.)
As others mention, the current foam is not the same thing and you’ve been able to buy small cans of spray foam for sealing the frames around doors and windows, etc. for decades.
The best time to do this would be if you were doing major renovations that included ripping the interior side of extrior wall gyproc/plasterboard off. Ensure all the utilities are up to par, then fill with foam. Worst case, you do this one room at a time. Obviously if you just drill holes top and bottom and fill the interior between two studs, there’s no guaratee you get the same complete fill and seal.