I have read elsewhere that spinning mercury would be used as the mirror.

The suggestions that I've seen for astronomy on the far side of the Moon have largely been about radio astronomy rather than optical. The lack of the ionosphere which otherwise blocks and distorts 10 meter and longer radio and using the Moon itself as a shield from the radio noise of Earth makes it more interesting.

Radio telescopes only need a wire mesh to deploy (rather than polished optical mirrors). https://www.skyatnightmagazine.com/space-science/arecibo-tel... has a view under Arecibo.

https://www.nasa.gov/general/lunar-crater-radio-telescope-lc...

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The liquid metal mirror telescopes https://en.wikipedia.org/wiki/Liquid-mirror_telescope are interesting in part because you can get liquid mercury temperatures near room temperature on Earth.

It's theoretically possible for the moon - https://ui.adsabs.harvard.edu/abs/2007Natur.447..979B/abstra...

    A previously proposed liquid mirror telescope, based upon a spinning liquid metallic alloy, is not appropriate for infrared applications, which will require a liquid below 130K. Here we report the successful coating of an ionic liquid with silver. The surface is smooth and the silver coating is stable on a timescale of months. The underlying ionic liquid does not evaporate in a vacuum and remains liquid down to a temperature of 175K Given that there are ~10^6 simple and ~10^18 ternary ionic liquids, it should be possible to synthesize liquids with even lower melting temperatures.