The question should not be when and how often Nuxwin is on vacation. I like being on vacation myself very much. Also, I'm sure most people would agree that he spent a whole lot of his free time to maintain and improve i-MSCP.
However, while maintaining this project on your own is not an easy job, it is also not very easy to contribute to i-MSCP. I'm almost sure that some of the i-MSCP users would be happy to contribute little things, like bug fixes, updates, translations and stuff. But, it is completely non-transparent what the last development status is, how the roadmap looks like, or where and how to contribute. For an opensource project, getting users in is the way how you distribute workload, which then allows you to be on vacation without worrying whether a bug or security issue needs to be addressed.
Maybe you are familiar with the bus factor (https://en.wikipedia.org/wiki/Bus_factor), which I assume close to 1 for the i-MSCP project.
Nuxwin I don't know the reasons for your way of developing i-MSCP (i.e., using private git repos), but maybe you are open for a discussion or interested in getting people in to support you?