I have a Lenovo T16 laptop. Assuming 200W/m² for a solar panel, if the lid had a solar panel on the back it could get about 18W if left in direct sunlight.

Maybe enough to run the thing in the sun if you're not doing anything too power hungry, but not enough to also charge.

I had a dream that some small child left a laptop outside to "charge in the sun" because that was (in the dream) a common idea for children's toys. I wondered how viable that would actually be.