I've used a Take-a-Look sunglass mirror for many years. It's so useful.

I have to lift my head slightly to see straight back along the road. Then a slight head turn sweeps the viewpoint from side to side as needed. So it's not a continuous monitoring mode, I have to specifically decide to look behind. That rear view is fast, easy and kind of automatic now. (some years ago, before I retired, I heard a strange noise in the hallway at work. I turned my head slightly to get a view in the mirror, without thinking. No mirror of course...)

Since the view is moveable with a slight head turn, it doesn't need to be wide angle, so I can see far back on the road. Convex handlebar mirrors are only good for objects nearby, but that's kind of useful.

It's so much better for left turns -- I can arrange to move over when there's no cars overtaking. Rough pavement at the edge of the road? ride in the middle if nobody is near. Riding on a curvy hill road--I'm out in left tire track,blinky going, checking the mirror a lot. If a car appears behind me, I can quickly get over to the right tire track, but being out in the lane gives the driver an earlier view of me.
It's also helpful when riding with other riders -- are they nearby or way behind?

I occasionally ride the local bike share bikes in the city, and don't have the mirror with me. That's really weird to have to turn my head to look back! Unsettling.

Cameras won't be helpful -- even if you can see the screen in bright sunlight, the wide field of view makes cars really tiny that are just a few seconds back. And you can't watch the screen all the time.

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"Stealth" car approaches
At any reasonable speed, there's too much wind noise to reliably hear cars behind me. Some tires are noisy, some not.
The mirror doesn't solve this problem, since I'm not actively looking back all the time. I do have a habit on quiet roads to use the mirror a lot when there's a curve or small rise ahead, or a car approaching from the front -- any time there won't be an easy passing situation for a car behind me.

Radar! Some of the local riders have the Garmin Varia radar. It's astonishingly effective. Usually it's beeps are the first indication of an overtaking car, before any of the group riders notice it. It has very few false alarms too. I considered buying one, but I'm usually riding with a group of 3-8 riders,which helps with traffic. Maybe soon -- and if I rode solo very often, I'd get one!

video review: https://www.youtube.com/watch?v=Bmdz_6ZpcIQ#t=1s and https://www.youtube.com/watch?v=0HBNXEFRLFA#t=1s

The Varia triggers on vehicles (and usually cyclists) that are closing the gap behind me. Cars (or cyclists) that are maintaining my speed don't need or get a signal.
It works with Garmin GPS computers, and there's a free phone app too. Riders mostly just listen for the beeps, instead of monitoring the "dots" showing the progress of the approaching cars.

Daytime blinkies (front and rear) for an early "heads up!" to drivers -- there's a cyclist way down the road, get ready.
My Cygolite rear 150 lumen blinky is on the 2-flashes-a-second single, sharp flash mode. That short flash is extremely bright, even in noon sunlight. It's instantly noticeable to me when some of the other riders are way ahead, too distant to make out as "a cyclist".

This single flash mode uses very little battery. I think it's 15 hours or so, compared to a couple of hours when on continuously.