That's aggravating the problem. No only the original way was painful, but now there are multiple ways and to the newcomer that just needs to contribute to a project - it's all one big mess.
Agreed! I pick up Go a few times a year (which doesn't help, admittedly) and even consulting the official documentation, it's hard for me to figure out what the current, correct way of doing things is.
If you want to learn this my suggestion:
Dedicate 30m to read https://blog.golang.org/using-go-modules and try it out with a small demo project,e.g. write a small tool that emits a uuid; keep the toy project very small so you don't encounter other problems that might distract you from learning the basics of dependency management.
Search for dependencies using pkg.go.dev.
That said there may still be projects out there that are unmaintained or the author didn't bother to convert to go.mod, so you might occasionally still encounter GOPATH.