For options that are supported by multiple different commands, such as --watchfs the anchor always links to the same text, so there's no way to link directly to a specific one, only the first one:

https://docs.bazel.build/versions/main/command-line-reference.html#flag--watchfs

Search that page for watchfs to see the other instances. Normally this isn't much of an issue because the docs are often the same for the same flag under different commands, but in this case the startup option is the first one and it's deprecated, while the build option has the more updated docs.