Also anything you generally find relaxing that isn’t intended to be.
For reasons I cannot articulate, I never liked intentional ASMR videos, but give me an upload of a three hour video course about a word processor from the 80s or a training video about how to take a sonogram of the kidneys and I’m all in.
As for generally relaxing stuff, for some reason I find recordings of radio comms, like storm spotter nets, to be relaxing. Also local news coverage about major weather events.
And to you UK lemmings I know about the shipping forecast.
Some beekeeping videos are restful. Here’s an example: https://youtu.be/Rd1HaPQZ4eU
He’s got a gentle voice and handles the bees gently, and they’re calm too. I’m a beekeeper and find this kind of video very soothing. I love the sound of a busy, happy hive. A lot of beekeeping videos are too shouty, with loud music and perky commentary drowning out the bees.