export image quality

Compare in a web browser the result of the export from Photoshop vs. the uploaded image, downloaded from the social media site. This will isolate if the issue is with the platform or Photoshop.

I would preferably export as PNG and not JPEG.

Also if you are reducing the size you better can do it with Image size function where you can choose to get a crispier image than with the size reduction at the export.

Attention!!! many platforms such as Facebook and Instagram use algorithms to reduce the weight and quality of images, so it is good to know how you proceed and which social networks you use.

Please read this (in particular the section titled "Supply pertinent information for more timely and effective answers”):
https://community.adobe.com/t5/using-the-community/community-how-to-guide-tips-amp-best-practices/td-p/11601738?page=1

Please provide relevant information. 

Which image formats, which pixel dimensions, which export/save processes, which social media platforms, …? 

What are the actual requirements of the social media platforms?