There are some more, if you can search.
Not all so called 5.1 in YouTube are surround, but just PCM stereo, check for the codec from settings, if the codec is e-ac3, it is 5.1 and will display as such in your surround system. My Sonos system decodes only AC3 Links as surround.
There is one channel 4k clips and trailers which has clips in 5.1 but it's highly compressed and hardly any dynamics neither strong bass. And the volume i had to bump up to reference to hear what I usually listen to at -20db.
As of now it's a flop for me..