first of all there is no voltage that are too low, lowering it may result in a crash but it will not degrade the gpu in anyway, it's called undervolting and there are plenty of guide on Youtube on how to do it.
however it is possible to damage your gpu by putting too much voltage in it, tho AMD has put a sotware limit (it can be increased to 1.25V i think, and the frequency limit of 1850MHz can be push up to 2100MHz) to prevent user to damage their gpu, so even at 1.2 V you are safe, but i wouldn't reconmend to go much higher than that.
i have a rx 5700 pulse and i can undervolt it to 0.9V at the stock speed (1750 MHz) and still be perfectly stable, no crash so far. undervolting is a very noce way to reduce temps, fan speed noise, and power consumption. for example, i droped 10°c on the gpu while lowering the fan speed from 1700rpm to 1300rpm and the power from 150w to just over 100w.
to undervolt you just need an gpu stress testing tool, i used heaven benchmark and lower the voltage 10 by 10 mV while runnig the benchmark until the gpu crash or gives artifacts, after that you keep the value that it crashed to, and add 20 to 30mv to it, to unsure that it will be stable.