Serfs were far better off than chattel slaves. A serf could not be sold away from their village, they could marry (AFAIK permission to do so was not required in most countries) and have a stable home with a spouse and kids, they had rights to the land they farmed, and could own property. It did vary between countries, and what you describe is true in some, not in others.

Serfdom declined over time in western Europe and had largely disappeared by the end of the middle ages. So it does not explain why western Europeans not invent the bicycle in that period that was at least a few centuries, sometimes longer - 800 years in some places!

> So it does not explain why western Europeans not invent the bicycle in that period

They were too busy fighting wars, like the 100 years war. Also the Inquisition might not have seen bicycles with good eyes. The bicycle couldn't have happened without the Reinassance and the Industrial Revolution.

The rule of thumb is that in Europe, it got worse as you went east. E.g. in Russia, the serf could be sold away from their village, and even away from their family, could effectively be stripped of any property by the owner, could be severely punished for arbitrary reasons. Just about the only thing that wasn't legal was outright murder - but even that was effectively unenforceable except in the most egregious cases involving numerous murders and torture, such as https://en.wikipedia.org/wiki/Darya_Nikolayevna_Saltykova.

In general, in many cases, what rights exist on paper is irrelevant; what matters is how they are applied in practice, and what avenues to enforce their rights the holders have. E.g. it is not uncommon for societies with serfdom to limit the ability of serfs to file legal petitions against their owners.