The brake lights on your on-screen car do show what’s happening outside. I find the display to be excessively subtle though, and I have to watch it closely to see it. Unfortunately that is usually also when I am closing in on traffic and should have my eyes *outside* the car.
But there is a “deceleration “ threshold which triggers the brake lights to turn on when using regen. I forget exactly what the number is, something like 0.3 G.
Edit: just noticed you have an X and I’m assuming my 3 is similar... this has got me in trouble before...