Buying your first mechanical keyboard is the moment most people spend three weekends watching review videos. You do not need to. The decision is mostly about size and switches, both of which can be narrowed down in fifteen minutes if you know what to look for.
Size
Full-size keyboards have everything: alphas, function row, arrows, and the number pad on the right. They are the standard layout most people learned to type on, and they take up significant desk space.
Tenkeyless (TKL) keyboards remove the number pad, which most people use less than they think. The keyboard is about twenty percent narrower, leaving more room for the mouse. For most users, TKL is the sweet spot.
Sixty-five percent and sixty percent boards remove the function row and (for sixty percent) the arrow keys. They are compact and beautiful but require learning key combinations for things you currently press directly. Worth considering if desk space matters; not for first-time buyers.
Layout
Get the layout matching your country. ISO layouts (UK, German, etc.) have a tall enter key and an extra key beside the left shift. ANSI layouts (US, most of Asia) have a wide enter and no extra key. Mixing them is uncomfortable for typing speed because the muscle memory carries over from your laptop.
Price tiers
Under a hundred euros: usable mechanical keyboards from brands like Keychron and Royal Kludge. Plastic case, decent switches, basic stabilizers. Most people do not need to spend more.
One hundred to two hundred: better case construction, often hot-swappable switches (you can change them without soldering), better stock keycaps, and quieter typing out of the box.
Above two hundred: enthusiast territory. The build quality, sound, and feel are noticeably better, but the difference shrinks fast as the price climbs. A four-hundred-euro board is not twice as good as a two-hundred-euro one.
Hot-swappable matters
If a board lets you swap switches without soldering, you can try a different switch family later for the price of one set of switches (around forty euros) rather than a whole new keyboard. For a first board, hot-swap is worth paying a small premium for.