MacOS after change of Motherboard If I want to change the motherboard of a MacBook with a new one and I install on it the same SSD I had on the previous motherboard that has installed the OS and everything.

When I boot the Mac with this new motherboard, do I have to re-install the OS from scratch or all my datas remain on it?
The OS is installed on the SSD. Most installations are non-specific: they will run on any Mac that the OS supports.

In any case: reinstalling the OS normally leaves your data intact on the volume. And you've got a backup in the event of something going wrong and your files being accidentally deleted. Of course you have.