Watching a local builder show - Azec has an exterior corner board that has no seams. I've never seen it before but it's cool because it never needs to be painted, it won't leak, it can be powerwashed and it doesn't look like vinyl. It looks like they also have window trim kits but I didn't catch that segment.
https://azekexteriors.com/products/t...s/cornerboards
https://azekexteriors.com/solutions/window-surrounds