Thy syntax highlighting for this in VSCode is just wrong. <repo_link>#branch is still perfectly valid, no need to worry, see lib_deps — PlatformIO latest documentation.
I was not clear enough - I am referring to the tree list to the left.
Unibridge is listed as a Github repo with its branch “New-core” and the list of changed files below, but the eModbus line just has a small list icon in front, “lib” behind it and a yellow “M” to signal modifications. I am missing the whole Github Monty here like Unibridge has it.