The 8h/day rule is an average per week if you are working 6 days a week, this is because the maximum work per week is 48h. Usually you work 5 days, so you fall in the rule that you must not be above 48h/week and a maximum of 10h/day.
If you work in shifts, some other rules apply but at the end, you cannot go over the 48h/week on average and have special "recovery" days.
But in Germany you have a lot of agreements for let say metal workers or people in the chemical industry. In some cases, the official week is only 37h or even 35h long.
It's actually even more involved than that. For example there needs to be a 24 hour down period per week and there are mandatory breaks an employee is required to take by law (refusing to take a break, even voluntarily, puts the employer in violation with the law).
I'd say that other than civil servants, people working in the "Handwerk" (a German concept that includes various industrial jobs and skilled crafts, literally "manual labour" but often implying specialised expertise) have it best as they typically work under union contracts and have fairly tight regulations.
OTOH loan workers tend to have it worst: loan workers bypass a lot of the labour laws and often get all of the drawbacks of being self-employed without the benefits of actual free agency. They're often hired to replace permanent employees, so they're sometimes met with hostility from their colleagues and they have no job security and often no way to transfer to a permanent position (both because that's often exactly what they're there to replace and because they're often under non-compete contracts that forbid them from doing that).
Agency work also tends to be pretty bad, especially for designers: you're often expected to work unpaid overtime and there is a lot of pressure keeping people from exercising their rights or asking for a raise. I've routinely seen designers work weekends and massive overtime (think 12 hours, not 10) for months on end. The worst story I heard was of a 32 hour day (working on a regular day until the next morning and then leaving "on time" the next day).
Note that not every agency is like this, but they exist and it's taken for granted that you have to "eat dirt" if you really want to work in the industry. This especially used to be a problem with internships but thanks to some changes to a few laws interns have it pretty good these days (e.g. "voluntary" interns have to be paid minimum wage, making them a lot less cost efficient than they used to be).
Also, of course, almost none of the labour protection laws apply to leadership roles (typically C-level jobs). The reasoning behind this probably being that if you run a company having to take time off can get in the way. Sadly this also means there are some strange corner cases for founders (e.g. you get almost none of the maternity protection).
If you work in shifts, some other rules apply but at the end, you cannot go over the 48h/week on average and have special "recovery" days.
But in Germany you have a lot of agreements for let say metal workers or people in the chemical industry. In some cases, the official week is only 37h or even 35h long.