I create rare, valuable information that saves people money and headaches. On a good month, 2% of my revenue will come from donations. Usually, it's 0%. At best, it pays for a meal and a beer. This website has 135k page views per month.
If that's how much I get from teaching people how to navigate German bureaucracy, I doubt you'll make anything from your opinions alone.
I insist on keeping the content unconditionally free, and donations don't work, but affiliate marketing does. I help people navigate certain boring purchases, so it lends itself to that sort of monetisation. I'd be recommending those products and services anyway.
Unfortunately, it incentivizes dishonest recommendations and passing ads as content. I chose not to do that, but I know I'd get paid more to recommend the wrong things. Since it's blended into the content, you'd be abusing people's trust in your content. At least banner ads were separate from the text.
I do not offer services either. My goal was to help as many people as possible, and that would go against it. Information should be free, especially when poor people need it the most. I also want the website to run itself. If I wanted to be on the computer full time, I'd just get a job.
And having some experience with German bureaucracy and taxes, and also having never lived in Germany nor speaking German, I'm fully aware how convoluted and complicated this can be and I could definitely see myself donating/paying for useful information if I didn't have a good accountant at my disposal.
I agree, on the grand scheme you won't make a whole lot but even with a population of 83 million, even if you add another 1 million like myself, your content still fits a relatively narrow niche. I'd love to give some advice but I honestly have no idea.
Affiliate marketing works well for my niche. I wanted to start similar sites about other topics, but if those don't naturally lead to certain purchases, they're extremely hard to effectively monetise.
In general, the internet got incredibly annoying, but I can understand why. Part of it is because we feel entitled to free content. There are few business models that allow people to be rewarded for their work while still offering a product for free. It usually involves selling something the user's data or attention.
I am personally against it for my website in particular though. I insist on keeping everything on it open and free. Immigration advice should help everyone, not just developers with a generous relocation bonus.
I'd much rather invest the effort into making the content more navigable/discoverable. This is actually what I'm working on right now.
Again though, this is just personal preference for this specific website. Selling packaged information could work. I did buy a motorcycle travel book that was a rehash of the author's YouTube channel.
The website mentioned above is more of a "visit it when you need it" resource. It's painfully boring to read, as it's written like a plain English instruction manual. It wouldn't be an interesting book.