I think this is basically a non-issue in practice. People with such iron-clad non-competes typically either a) take a non competing job, or b) work on something anyway. The latter effectively means the original company funds some research.
If you do this with say, sales people, or traders, or whatever, it shuts down their work. If you do it with engineers they'll just make something at home.
Every now and then I see someone comment on HN about their experience with longer between-jobs periods, sabbatical, etc. The core theme I've noticed is that, apparently, it's common to "waste" some 3-6 months before one starts making good use of their time - apparently this is how much it takes to properly switch over to being fully self-directed.
If that hypothesis is accurate, then it's not surprising you've built "nothing worthwhile" during your five-month break - you've got yanked back into employment right as you were finally ready to make good use of your time!
Only a tiny portion of truly critical positions would have compensated non-competes under this system and the rest would have no such blocks.
It's called the same thing in Germany. The term also applies to when you quit, but the employer wants to cut your access to the company ahead of your contract termination date. It's typical to have 1-3 months of "notice period" in Germany.
Usually the way it works is that when you resign, the employer has a fixed amount of time (specified in your contract) within which to decide whether to exercise the noncompete, and for how long (i.e. they could elect a subset of the maximum term in your contract), and once exercised, they can't change their mind. If you violate the noncompete, they'll of course stop the payments, possibly claw back payments, keep your deferred comp (which they are holding over your head during the noncompete), possibly reset the noncompete clock (so you have to start waiting all over again), and possibly sue you. Details will vary, but broadly that's my experience.
Some consider it one of the major perks of the industry, assuming you become important enough to have it exercised on you, and would be sad to see them banned. Firms consider it money well spent, which makes sense when you consider that investment strategies have no real protection as intellectual property... copyright is only narrowly useful, patenting would mean disclosing, and so at the end of the day they are just trade secrets, which can really only be protected by nondisclosure and noncompete agreements.
This sort of a non-compete would almost have certainly resulted in Zoom not being built.
I imagine this would be functionally equivalent to a ban on non-competes because it seems like it'd be an insane waste of money but if a company wants to provide a paid vacation on the way out I see no reason to stop them. Unpaid non-competes should be illegal as somebody's right to earn a living trumps a corporation's right to impose an unconscionable contract on its employees.