Just to clarify, I was never a developer of Passbolt. I think they based their repository off of CakePHP (which I do maintain) and inherited all the commit history that way.
https://github.com/passbolt/passbolt_api/graphs/contributors
What I'm working on are developer insights and I've found the most intuitive way to look at contributions is to sort them by latest commits.
With this type of display, you can quickly see who is contributing on an active basis, and for how long. A good example would be the vscode repository.
Here you can see a lot of developers have been contributing on a steady basis for quite some time.
Wish you all the best with your enhanced developer insights.
The last contribution was over 4 years ago (first contribution was 12 years ago), which would be the remnants of the fork.