Does anyone know the URL for this assuming it exists?
For Node-Red I wrote a small device driver ([RELEASE] Hub Information Driver) that exposes it. Node-Red uses MakerAPI as its endpoint provider - same method could be used directly if you chose.
Could also use it with an RM or webCoRE endpoint.
Do you happen to know the URL for getting the version via MakerAPI?
You would get it via the get device info url for your maker instance (Maker API - Hubitat Documentation)