Feel free to share ideas and tools to make multiple versions of your art.
I think, for titlescreens and backdrops, the online tool Dithertron on 8bitworkshop is a big help, since it not only converts the colours but also sticks to other technical limitations of each platform. Very useful.
For sprites, you can find a lot of palettes for the classic platforms at https://lospec.com/
Then it's just a matter of importing them into your favourite graphics tool and convert. But you'll have to know hardware limitations yourself, like sprites only having 3 colours on some platforms.
If you decide to try this with some of your art, please do post each version here as an example. I'm curious. :-)