Something dropped a whoooole bunch of seeds. No idea what it was?

The greenery looks like cotyledons. Actual leaves that emerge might look totally different.

Any Norway maples nearby?

Yes, there are maple trees nearby! I just did more googling for norway maple seedlings and that's exactly what it is (I find the leaves and wing looking things all over my garden). Thank you so much! Now on to figuring out how to tackle this

I just use my handrake to loosen them from the soil - if you get to them at this stage, the root is still shallow. I have tons of them at this time of year! As long as you don't let it go too long, you'll be fine :).

Shade gardening usually involves annual removal of some kind of tree seeds.