Based on the flight times and 100 mile flights ~100 miles off the coast and the investigated boats in the area...they couldn't be small. At least not with current consumer battery technology. Maybe if they were launched by a sub?

There's a youtuber that has a multi-hour autonomous drone, but it's solar powered and this was at night.

Hybris electric/gas drones are commercially available these days.

https://dronelife.com/2021/03/18/skyfront-gas-electric-hybri...

That could almost had done what’s reported from land, and easily from a small boat 50 miles away from the ships (which is well over the horizon).