Adobe Spark Post looks great during the creation process, but when I export - both as a png and a jpeg, the quality is awful. I would be better off taking using Windows Snipping Tool to grab an image of the finished project rather than downloading the export.
It makes edges of logos very jagged and blocky - even unreadable, and massively decreases the quality of images, even though the final exported pixel size is pretty decent.
Why is this, and how do I fix it, because it's making the tool unusable when the exported image is such poor quality.
Spark is never going to generate "print quality" images because that's not what it was designed for. Spark generates highly compressed, web quality graphics. Try downloading with a better browser -- Chrome, Firefox or Safari. Don't use MS Edge or IE. See this related support article.