Wouldn't they be able to find that out from LinkedIn or social, for perhaps the majority of tech people? Not saying that you use social media, but it's possible they find out.
I think if you've got any sense then you'd leave your LinkedIn profile unchanged until the exclusion period in your contract runs out. The "non-compete" clauses in mine have always been around 2-6 months, they were never enforced. I binned LinkedIn so it's not a problem for previous employers to spy on me, and my social media content never mentions anything about work things.
For other social media then just keep your nose clean and stick to posting content and discussing stuff that doesn't mention work.
But that said unless you stole your previous employer's crown jewels (customer lists, source code, IP etc) then these clauses would get thrown out if you were taken to court. Imagine a Volkswagen car dealership trying to limit, contractually, the employment opportunities of their mechanics or sales people from moving down the road to the Ford dealership for better hours/pay/commission. They'd be laughed out of the court room I think.
In almost every case you're correct. If its a hobby project, or it allows you to make a normal living you're likely to be fine. The danger comes when you end up founding the next facebook and there is some real money involved. Then you might have the Winklevii suing you based on the clause in the contract.
They could get expert testimony about the amount of time it took to create, find old stack exchange questions let alone get court ordered access to git etc. They may not end up winning, but you could settle just to avoid the cost.
On the other hand, this definitely counts as "nice problem to have" and probably isn't worth actually worrying about.
