The one I have now seems to do 100% and then nothing in an alternating pattern to achieve 50%...I don’t know if it’s really doing that
If it sounds like it is doing that, it is. On ten seconds, off tens seconds, on ten seconds, and so on.
The ones that can be dialed down to deliver a constant lower power are called inverter microwaves.
I have the on/off/on/off… type. There is a trick to get actual low power to your food, for smaller items. Put a bowl/measuring cup of water in the oven with the food, and part of the power goes to your food, part of it goes to the water.
Neat trick, you can imitate 50% without doubling the cooking time.