>>3389897Instagram only supports 1080 on the x axis. So ideally, you should resize your image to be 1080 wide. I made an action that actually helps a lot in ensuring maximum sharpness when doing this downsizing, sharper than what you're able to get with a standard lightroom/photoshop downsize.
Here' the shameless plug of my own video. But it should help you if you're interested. The info starts at 1:55. And the end result comparing photoshops resize to the action I made is at 9:45
https://youtu.be/vPPy7PMqpVY?t=115 