When ever editing big text projects I used $\Latex$ . Just because Latex is the right tool for the job.
But as it turned out there has been a simpler tool for the job. And it is called Typst.

Why it is simpler:

• It is FOSS
• Ready to write: no \document{begin}
• Markdown based syntax where it can: eg. headings with =
• Easy math syntax
• Simple coding constructs instead of single use case based macros
• FOSS templates ready to clone
• Renders preview from buffer: instant update without having to safe

Their GitHub Page