Can I Use This Old Toy Drone Battery for My Whoop?

Probably not - at least not without modification. Likely unwise unless you know what you're doing.

Maybe, but it's gonna suck

I mean, it looks like a 1s Li-Ion battery so odds are strong your drone isn't going to work worth a crap.  The rating is probably terrible as well.  Botgrinder did something like this with old e-cig cart batteries once.  Needless to say, it sucked.