I've had to edit typst recently and I used

https://codeberg.org/meow_king/typst-ts-mode

And the LSP: https://github.com/Myriad-Dreamin/tinymist

Specifically for doom, you'd add typst-ts-mode in your packages.el in a package! entry and check either eglot or lsp-mode doc for how to configure the LSP.