While System Accent color is probably the way to go (and probably easiest to implement), I would suggest a default color that is a bit brighter and that stands out a bit more. Or even consider color and bold text.
I, generally, don’t use dark mode frequently, if at all, and brighter would be better, and bold even more so, especially in light mode.
The headings are already bold, so I don’t think we need to make them bolder. In our testing, the colour looks great in light mode as well. It really stands out, so I think you’ll be pleased when you use it