Hi Tony,
I started disabling more and more apps and it appears like it was what you said, a network monitoring app running in the background that was the culprit. I was able to start uploading files again so I think my issue is resolved.
For the record, the app was NetWorx. I have the same app on my other laptop which was uploading properly so I’m not sure why it was blocking the connection on my desktop computer, but nonetheless now that it is removed I can upload.