The "magic vs tech" conflict requires careful forethought to avoid the problems pointed out in this thread. Now, one explanation I've seen is that magic is EMP. You can see this in settings like Amethyst. The magic only interferes with electronics, but not purely mechanical technology. So gunpowder and steam still works just fine, but computers fail.
In order for magic to interfere with steampunk, you'd need to invent new physics just for steampunk that magic interferes with, like the ether I mentioned. It's not as complicated as some are making it out to be. If real EMP can negatively affect electronics without making your head explode, then you should be able to use the same logic for fictional physics. Now here's the idea I had for doing that:
Steampunk relies on combustibles, right? Wood, whale oil, fossil fuels, etc. So... lets replace the fuel source with a magical equivalent. Instead of coal, gas, and oil, fossil fuels and gunpowder on this world are made of concentrated "ether". Meanwhile, magic is powered by "magicules". Both ether and magicules are naturally occurring and are required for natural processes in trace amounts, but when their concentrations increase they interfere with each other, like trying to dowse a forest fire with a bucket of water or drop a molotov into a lake, despite humans needing both water and combustive processes to survive. Trying to cast a spell on a train would cause the ether engine to malfunction, while trying to fire a gun inside a ritual circle would cause it to shoot a blank or explode in the hand.
