I've never heard of this type of judgement. Was this in the USA? What was your uncle's crime?

Happens quite frequently from what I'm told. Judges have quite a bit of discretion sometimes and try to sentence intelligently.

[anecdote] I used to know someone who was an addict. Judge gave her the choice of going on probation for a year, or 45 days in jail. The catch was if she took the probation offer but was picked up for drug offenses in that time, it was an immediate sentence of a year in jail.

She took the 45 days. Better the devil you know than the one you can't control! [/anecdote]

This was in the US, Pittsburgh, PA to be specific. However this was during the Vietnam war. Googling around, this sort of arrangement would make one ineligible from enlisting nowadays. There's an article referring to at least one case in which someone was denied enlistment[0] because of just such a case. Further research indicates that this is asked of recruits, meaning one could hypothetically perjure himself and maybe not get caught. I couldn't find any other references to this happening today, but there were loads of waivers issued back in the days of "the surge", so it wouldn't surprise me if some folks slipped through the cracks and got a "jail or enlist" talk from a small town sheriff or magistrate.

[0] - https://www.stripes.com/news/judge-said-army-or-jail-but-mil...

Hear of it at least 2 dozen times, various states, usa. Seems a bit less common now, but still happens. Usually for when a judge wants to give you an out. If you bail, you get full judgement.

sounds like GoT, take the black or be executed. Still, I think this is a point in favor of conscription - there's a big generation of young adults that don't learn how to adult anymore, basic stuff like laundry, ironing, regular exercise, (self-) discipline, etc.

If young adults are getting by without knowing how to iron, I suggest that says more about ironing than it does about the adults.

Why not have a laundry course then? Why force people who don't need it to waste time there?

The point isn't that they didn't learn to do laundry. Fixing it by offering a laundry course is just putting black tape over a warning light. They didn't have the environment growing up that made being an upright citizen easy or particularly likely. You can't teach a course about "responsibility" and expect good things.