Instagram is a multibillion-dollar company owned by another multibillion-dollar company. It is, essentially, a photo-hosting website.
You cannot upload photos from your browser. Unless your browser is a mobile browser (what's the difference? no one knows). Unless your mobile browser is in portrait orientation (why? no one knows). Unless your images are jpeg only (in 2020? why?).
And it doesn't even let you to properly upload a photo. It only lets you add a photo/video to a story.
Because screw you that's why.