The Aeotec multisensor six or seven can run off a USB cable. Waterproofing isn’t great, it’s only IP 20, so you would probably want to put it inside a clear plastic box, maybe an outlet cover protector.
Plus something like this. This is just a typical design.
https://www.amazon.com/TayMac-MM410C-Weatherproof-Receptacle-Protector/dp/B001JEPX44/
There are also ways to do it with a sonoff basic by attaching a light sensor to that, but I’m hesitant to recommend starting down that path until the transition to edge is complete.
And as I find myself saying a lot recently, personally, I am putting off most device purchases until we know more about how matter is going to work. If everything happens as it should, there should be a lot of new devices available that will work with smartthings locally without requiring any custom code. But they’re not here yet, so it depends on whether you feel like waiting.