Also, if you think that there is no personal liability for the managing founder in a limited liability company, don't search for "Geschäftsführerhaftung" or you are going to have a bad day.
This is not a German exclusive. Managers of a company are nowhere shielded from legal responsibility when they violate the criminal code. (Okay, big banks maybe not, but at least from the letter of the law...)
That supermarket down the street? Almost surely run by a fully liable merchant. That consulting office next door? A fully liable partnership. This two-person software company? Both owner fully liable. It's a common choice and often better suited than it might sound at first.
Furthermore, it's better to control risk by getting the proper insurance for your business and NOT relying on "limited" liability of a GmbH (although I heard you have to do pretty dumb shit to really be held liable personally in a GmbH).
So I'm really wondering what you did that you almost ended up in jail. This is certainly not the case for 99.9% of all people who just want to file taxes on their Adsense income once per year or code HTML for a bit of money.
https://en.wikipedia.org/wiki/Debtors%27_prison
(Note that the US is often criticized for court fines which result in jail time if you're unable to pay, but that's a much later meaning. Originally it meant jail if you were unable to pay someone back.)
The problem with this is that often it isn't entirely clear if a company really is bankrupt by that definition. A company can be nominally bankrupt in one moment and solvent again in the next depending on how you look at it from a technical / accounting point of view.
This again unfortunately sometimes is preyed upon by both liquidators, investors and creditors, who might try to sue the managing director in order to recoup their losses from the director's personal funds. A conviction for delayed filing of bankruptcy both applies additional pressure and makes a director personally liable, GmbH or not.
So, in short: No there are no debtors' prisons anymore but the effect you described very much still applies thanks to outdated and misguided German bankruptcy laws.
So? You are personally responsible and liable for a nearly everything you do in life. Typically, you'll only "go to jail" if you do something seriously wrong, and then the limited liability of a GmbH won't save you (whether you're an owner or an employee).
The limited liability of a GmbH refers mostly to financial liabilities in case of bankruptcy, not to, e.g., criminal negligence.
This costs you 10 minutes and 25 bucks (Gewerbeschein). Then you can file taxes for your side income once per year, which takes another 30 minutes, because at the side-income level the calculation is: income - expenses.