@tutoriales-honestos asked again here, and I have redirected followon conversation to this original Topic.
The quick answer is still that you can use a UDL, as I said in 2022.
However, I had forgotten about this discussion, so I had started researching an answer to the ask-again Topic, and discovered that the SciTE testbed-editor will open Go/Golang (*.go) files and internally use the C++ lexer (LexCPP.cpp). The cpp.properties includes definitions for Go. So it can handle it.
I am going to point this out in the long-open ISSUE #8090 that Alan linked, because with that, there shouldn’t be much overhead to add it to Notepad++. So if anyone pays attention to my reply there, it might be that it’s much easier to add that language than was originally thought.