I stand corrected
Wow - I'd have never guessed it was plastic

Still must hurt to break the corner with your head!!

 

Your broken corner is so small you might consider filing it smooth and cutting off the other corner to match

 

Here’s a possible idea. If you glued it back on and can still see the break maybe apply a strip of door edge or side protector moulding across the bottom edge. Black or chrome or stainless finish.

 

Just as further encouragement for a repair vs replace

We had someone back into our 2018 when it was pretty new. They put a small two inch dent in the center of the rear tailgate near the bottom. Noticeable but not big damage. Insurance covered it as the other driver was at fault.

Total cost after replacement tailgate, remove and refit, Re spray to match etc. $10,000. Yes - I'm not kidding
Massive labor costs to disassemble all the sensors, wiring, remove and install rear glass, heated windows, etc. Dozens and dozens of new fasteners, clips and plastic pieces. The order sheet was two pages long with little parts

I'm sure you could do it for less but a good quality spray job, I presume an auto glass place will have to fit the window in, lots of small parts and hours of labor.... I'd definitely suggest a repair. A good body shop should be able to do that for a few hrs of labor

 

If it’s composite or plastic how could it dent?
Is yours aluminum or metallic?

 

That's why I just assumed it was aluminium
But if you look at the photo below you can see the dent. Plastic can certainly dent as well as cracking or tearing

 

I'm just going to epoxy it back on. Should be an improvement over the duct tape that's holding it on now.