I’d visit a local Buick Dealer. Start at the Parts Department and perhaps the parts guy/gal will show you a parts diagram or an actual mirror assembly and you can learn what part/parts/assembly is/are available. That should take a little mystery out of it. Ask questions.
Next, I’d go to the body/collision shop at the Buick Dealer and talk with somebody there who can give you some idea of what repair/replacement involves, have them give you an estimate just in case it sounds to tedious for you.
I’m not sure which model-year Buick Encores have that identical mirror (same part numbers), but another option could be an auto salvage yard, specializing in late model cars. They should know which model/model-years interchange. There’s a chance you’ll find what you need and if you need a painted part, perhaps you can find one in your color. However, salvage yards sometimes like to keep doors complete to sell as a unit, but you won’t know until you try.
This will all give you some idea as to whether it’s worth fixing it yourself, paying and having a shop do it, calling your insurance agent and having them authorize repairs.
2018 Buick Encore… my advice is to fix it properly, to function and look like new, not Mickey-Mouse it with glue!