Using the new 2.90 version, I made a simple animation using some cloths sims and rendered it out in PNG images. When I check the images inside my file browser (Both the Blender file browser and the native MacOS file browser) I see that they are not PNG images. My mac instead says that they are TextEdit Documents.
When I open the image, it opens normally inside the "Preview" app (the default mac app for opening images). Sometimes it opens inside the TextEdit app and it shows me a bunch of garbled text.