Hi Derek,
Have you tried ConText? https://www.contexteditor.org
It hasn't been updated in a long while, but works quite satisfactorily under Win 10. I don't know about Win 11! I've been using it for more than 10 years!! A highlighter for MSTS .eng/.wag files is available from Steam4Me under Tutorials > Miscellaneous. A highlighter is also available from the ConText website but S4Me doesn't recommend it.
Cheers,
Ged