What to expect
Speed depends on the graphics card, not the age of the machine. Apple silicon Pro and Max and desktop graphics cards are the right fit. Integrated laptop graphics, Chromebooks and phones run the same conversion but can take hours on a 4K export, so use the 1080p preset there.
A 30-second export takes at least 2½ minutes on an M3 Max, plugged in, a floor, not a promise. Plug in: on battery, Apple silicon runs roughly an order of magnitude slower.
Chrome or Edge, with hardware acceleration switched on. That setting being off is the commonest reason it will not start. Firefox is untested and expected to fail.