Hey fellow spicy food lover @pepperaddict
As far as I understand from talking with the technical team on this, and it doesn’t seem like we have active CORS restrictions in place. I am not quite sure what might be causing this for the /files/ endpoint, to be transparent, and I will discuss this further with our team. I appreciate your insight and extra info to what is happening on your end - every little bit of info helps 
-Alex
Moderator edit: you can now upload files from the client-side using the monday SDK. Here’s an announcement on how to do it: Quick update: you can now upload a file from the client-side using the monday SDK. Check out this announcement for more information: Announcement: Uploading files to monday.com has just become easier :)