Might want to look into companies involved in refrigeration or coolant for electrical devices. Because although the claim is that LK-99 works above room temperature, "LK-99 is not able to carry much current in its superconducting state at these high temperatures", same for other superconductors. So, it may still need to be cooled to work reliably/efficiently, or maybe another superconducting material will be discovered that is easier to manufacture but has a lower critical temperature.

Not semiconductors (not applicable anywhere in how we make them now, relatively small technological advantage for existing companies), not transmission (low critical current), IMO quantum computing seems like an interesting option, assuming you can find a reasonably not-shady option.

Also, if any currently low-volume materials are needed suppliers of those should receive a nice boost.

I would probably just buy and hold Telefonaktiebolageta LM Ericsson (On the nasdaq: ERIC). It is a transmission line construction company. If room temperature superconductors are fairly cheap and real, then long distance transmission is going to be re-wired and additional marginal projects are going to enter the construction pipeline.

You can diversify this with companies such as TSMC and Samsung(better chips).

If electrical transmission is cheap, at least in bulk, I'd expect that countries that allow upgrading transmission lines will have cheaper electricity, using more appliances that consume enough power for that to be their main cost. So, HVAC. If you want a specific stock, how about Hitachi (HTHIY)?