Sometimes, and it's not been tracked down exactly, some dependencies of the site aren't built even though it says they are. In those cases, re-run yarn bootstrap and yarn build to re-build all the internal site deps.
By default the website runs without twoslash code samples being evaluated, this affects the syntax highlighting. To turn it on, use yarn start-twoslash instead of yarn start.
The Windows support for watchman is a bit meh. It's not likely to get better, given how well WSL works now. So, you could use WSL to work around that.
Though, for a lot of changes to the site: Watchman is optional. All the watchman script does is run yarn workspace [xxyy] build when you save in a package which is not typescriptlang-org (the gatsby website).
To run the site without watchman, use yarn workspace typescriptlang-org start.