it can not be done. It would reacquire a fauna as soon as you lay it.

For pots? Nuke it. Nuke it damp until it steams. Keep in mind that some spores are tougher than the microwave.

For mulch? See the previous reply.

You could sterilize very small batches of mulch, a soilless mix, or soil at a time in a microwave or other oven, just be aware that it can really stink up the house. Orchids grow in the wild in unsterilized soil all the time so there probably is no real need to do that. If you suspect there may be a disease pathogen that would adversely affect that orchid then don't use that material as a growing medium.

If you have a pressure cooker, 45 minutes at 15 pounds will do the trick.

Why would this be desirable? I'm not sure I ynderstand.

To keep it out of the house I have used a gas grill with compost in a cast iron frying pan. Be careful not to burn it. I used one someone was tossing out.

My intent was to kill weed seeds. While that did work, I am not convinced any of the good soil microbes return.

I vote for the microwave steaming. It's rare that you ever need to try to sterilize anything, but a small amount of potting medium for a finicky plant sounds like one of the times.

I think microwaving a palm tree sounds the best.

We collect fir and pine from place, put it in a metal barre, slap a lid on it, and cook it until it hits 170 degrees f. Kills bugs, many weed seeds, etc. Let cool, dump it in a metal wheelbarrow. Spray to cool, let air out. A little spray of water, voila. Smells smoky for a short time, high acid, good for many plants, like blueberries, raspberries, straw berries, etc. We check soil and mulch for ph, nitro, phospates, etc. Snails and slugs do not enjoy it at all. Less weeds, strawberries will touch down on it, not mud, and save on watering. Cheers.