I have some LED drivers that u have to use a screwdriver on the driver to adjust a pot so u can dim them. This is a terrible design for me. I was wondering what if i just used a Variac variable transformer to adjust the input voltage, could this work too?
i just tried it, and it didnt work
No, the driver module will try to maintain and then drop out totally (under-voltage crap-out).
Most such modules are designed to work with a large voltage range (90-250V is typical), producing the same brightness regardless.
They will work at lower voltages as well; how much lower depends on the actual device. So with 220V mains just 20% of the voltage may already give full brightness.
For the same reason traditional (phase cutting) dimmers also don't work.