Sadly, this seems to have changed. Several years ago the policy used to be that what you developed on your own time was your own, and even if you used company resources and spent time while at work on "your own" inventions, they still belonged to you as long as it wasn't an excessive amount. For example, if you printed out something or used a copier, or did a google search at work, etc. It seems they decided that was too good for the drones though.

Many Big Cos do. One reason you are often better off working for small companies. Risk is they can't always pay as well.

Can confirm. Was acquired and had to sign the same "we own everything you do even in your own time" agreement.

This isn't true. They own side-projects the relate to your direct job or that can directly compete with Amazon. If your side project is a compression algorithm and you work in website design, Amazon doesn't really have any right to your stuff.

It's actually a pretty standard invention agreement across tech companies.

That is a bery good rason not to work there. Thank you.

Is that enforceable though?

Doesn't matter what the courts say if the mere threat of a lawsuit can scare off investors in a future startup.

Pretty sure recently I read that this can't be enforced very easily (looking for source)

I guess the fine print in the employment contracts of most companies says so. The degree of enforcement might vary, though.