Here are the document sizes for Instagram: Instagram Image Size: The Right Image Size for 2019
You don't need to care about ppi, since only pixel dimensions matter.
Try PNG and if it doesn't work, try JPEG with different compressions
All social media services will further compress your images.
All of them will change constantly. So what is true about image sizes today might not apply tomorrow.
The compression they apply will have different effect on different types of images (e.g. it might look horrible when there are large red areas in your image, but it might be just acceptable with other colors).