Project architecture: how does the vendor folder depend on Composer and GIT?

Question

Composer

The composer system is convenient for me, because all the dependencies of the project are written in it, everything is installed automatically through it, then you can connect the necessary classes through "use", etc... And everything is stored in one place - in the vendor folder.
But now I needed to add my library to the project, and I did not add it to git.

How to do it right?
Options:
1. The simplest and most obvious is to add it to your private repository, register access to the repository, download it via composer. But consider the option without adding to github, so as not to bother with access to a closed repository (I have not encountered this yet).
2. Just create a new folder in the "vendor" folder, but what should I write in composer.json then? You won't write anything. It turns out that this local library should be kept in mind. Is that bad. Or is the vendor folder (the one at the root of the project) generally dependent and should only be managed through composer?
3. Create a folder with the library in another place, for example, in the folder of the project itself. But something is wrong here.

Any other option? How right?

Answer 1

3 option