Hi,
I have a problem with exporting simple graphics made in Designer to GIF - everything white gets artefacts. It doesn't matter if it's white fill in object or empty background. Also setting Matte to white or none doesn't change anything. Exports to PNG and JPG are fine. Opening PNG in Photo and then exporting to GIF (file A5) also creates artefacts.
I'm using v. 1.8.2 on MacBook Air with Catalina 10.15.4.