Remember that "Network Engineering Stack Exchange is for asking questions about professionally managed networks in a business environment." Notice that the example protocols are actual, real protocols used in business, and they are actually used to operate networks in business.
Your protocol is an experimental protocol for which there are no published standards, nobody here knows anything about it, and enterprise-grade network equipment does not support it.
SE sites are often confused with help sites, but they are not. The SE concept is that if you have a questions, it is likely that others have the same question, so SE created subject archives for such questions and answers, but the questions must be on-topic nd specific enough to get specific answers.
none of the stackexchange sites fit to this topic, although it clearly
seems to be a thing in anonymous networking
Not all questions have an SE site that fits.
how the engineer part in network engineering is to be interpreted,
because if it's just about using things that already exist, where's
It is about engineering the network, not building new devices or protocols (more of an IEEE engineering thing where they have ethernet, token ring, Wi-Fi, etc.). The engineering is creating a network topology with the proper enterprise-grade network devices and configuring those to get the desired result. If the devices do not support your protocol because it has not been standardized, how does that fit?
Also, notice that all "education, certification, or homework" questions are explicitly off-topic here. Your protocol could fall into that category, and none of us here know anything about it. For TCP, we can refer to the RFCs covering it and see the algorithms used for it.
One big problem you have it that IPv6 packets are not allowed to be extended in-flight, but that is exactly what you are doing. IPv6 is a protocol used in business, and you seem to be breaking it. There is a specific model for extending IPv6 (extension headers) and you are not following that model. None of that would be used in business, which needs consistent, vetted protocols.
Your protocol falls into the same category as things like Skype that are proprietary and are simply black boxes about which we cannot answer questions because we have no information on the specifics of the protocol.