Why does the quality of my pictures deteriorate after they are published?

[EtsyHuntOfficial]

I am using Pinterest for the first time. Have you ever had this problem?
I have followed the rule of 2:3 for my pictures. The image is clear before uploading, but the image quality will decline after publishing.

[thehalcyonhive]

Are you creating your pins using Canva?  If so, download them in .png format and increase the size using the slider.  This should help!