If we consider groundplane antenna, which should be much better than anything that you can fit on a HT, it might be centered on 145MHz (region 2 band) and it'll be good for 10MHz for 1:1.5 SWR (140-150) and 17MHz for 1:2 SWR (136.5-153.5) according to some random measurement, first that i found. Outside of these ranges SWR rises rapidly and if you tried to transmit on say 170MHz you might get SWR 1:5, perhaps 1:10 or worse if you're unlucky. On receive this doesn't matter too much because these nano- to microwatts of rx power would just bounce back harmlessly with the only effect being that apparent signal strength is lower. But if you tried to transmit then design currents or voltages would be exceeded and something will break, usually final stage of amplifier. This gets rarer than it used to be because some radios can measure SWR and will reduce power in such scenario. This also gets worse the higher transmitted power is

This happens because unlike on HF + 6m, on 2m and up ATUs are not a thing* and all antennas are expected to be matched. So you can use the same radio on GMRS or PMR or what have you and on 2m or 70cm band, but you have to change antennas between these uses. If you want to use all of these on one antenna, then there are special wideband designs like LPDA but this makes sense on a mast and not on handheld radio

* there are tuner designs that work on 2m and up, but you won't find them in HT, there's no point, they're too big, too heavy and too expensive

Even if you tried and made it to work, there might be other incredible problems with things like harmonics or other spurious emissions because filters were not designed to work way out of these frequencies. For example you can try to force Quansheng UV-5K (?) to transmit on 60-ish MHz but most of the power goes out at 2nd and 3rd harmonic, because of the way filters were set up. Narrowband designs are much easier and this is what you'll see all the time in amateur radio. Wideband and ultrawideband designs are constant source of job security for RF/microwave engineers

You can think of matching units and antennas (and to some degree even feedlines) as filters to some degree, because their bandwidth is not infinite