In summary, there are a few components not included in the public repository, mainly because it is very difficult in practice to get people to pay for a 100% open source tool where they can just clone it and remove any license requirement in a few lines. So it is not a fully Apache licensed application, it's core is. There is only one release version so it is difficult to provide a separate apache-only installer, mainly for technical implementation reasons. Some codebases can't be perfectly split into free and non-free parts that can be shipped separately. These not included components are the license handling implementation, the low-level shell process handling implementation, and the CI/CD scripts for distribution.
The EULA is just standard terms like don't try to circumvent the license requirement, if you buy a license don't share it with other people, some warranty and liability stuff, etc.
If you build a development version from source, it requires to have another xpipe installation present where it can utilize some of the shipped components from it. But you can fully run and modify that development version. They are not necessary for basic core functionality but it doesn't work without it as the license requirement could be disabled easily then as I mentioned before.
Overall I think this split is the best solution considering all factors. I understand that some open-source proponents don't like that. But I think since the application core is open source, it still has the good effect of establishing trust because anyone can take a look at how your data is handled internally, which is especially important in this context where a lot of sensitive information is used.