Hence why I use .txt and not .rtf (After having multiple RTF files become corrupted)

Syntax highlighting is definitely less complex than updating and rendering RTF and HTML.

There is configurable syntax highlighting in vscode.

Should an app like Notepad ever embed a WebView? (with e.g. tauri-apps/wry instead of CEF now FWIU)? Not even for a Markdown Preview feature IMHO.