Ask HN: How to experiment with a new OS approach?

This week, Daylight Computer announced what they’ve been working on. The distraction-free approach reminded me of the Mercury OS concept from 2019: https://www.mercuryos.com/architecture

And that made me wonder: how would one experiment with that kind of concepts?

There are of course plenty of open-source OSes but that seems like a daunting task to start from that. (to me at least)

Maybe a simple app (even a web app) that takes over the whole screen to explore ideas?

How would you approach this? What already exists in this area?

Thanks!