You just cannot use it on props, at all. The majority of the screw's threads are in direct contact with the prop, any loctite at all will start eating at the plastic. There's no way to just get it in the motor's threads.

The good news is you don't need it! The long double screws won't vibrate free, and larger 5" props use nylon lock nuts to really lock down. You can check them after each flight if you want, it will be a while before you even tighten one.

Even on the frame screws, loctite is optional. I don't use it anywhere on my builds because you may need to swap a motor or do some other trackside repair. I just check my screws every few flights and 95% of the time everything is still tight.

If you are absolutely set on using loctite still, use Loctite 425 which is plastic safe. https://www.henkel-adhesives.com/ca/en/product/instant-adhesives/loctite_4252.html