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!