CorelDraw designed Facebook png graphic pixellated

For the past few months, I've had a problem with my graphics designed for social media pixelating when exported as PNG. I am exporting these graphics at the recommended 1200 x 1200 and 1080 x 1080, both at 300 dpi. I've never really had this problem before and always had clean exports. I'm not sure whether this is Corel (desktop version) or Facebook compressing the hell out of the graphic. I have templates for all my social media graphics where the graphic is only about 3 inches wide. I get this pixelation when exporting at this size and taking that same graphic and resizing it to the proper size, and then exporting, and I still get the pixelation problem.

Any insight?  I've been a Corel Draw user for over 20 years. I'm not sure what could be going on.