You're trying to upload an extremely large file, which isn't currently supported.
Paste "4DNU3GRL" into the search bar in All Fields & Tags mode, and then delete that attachment and empty the trash. You can re-add it as a linked file if you want, but it won't work as a stored file if you're using syncing.
Upgrade Storage
Paste "4DNU3GRL" into the search bar in All Fields & Tags mode, and then delete that attachment and empty the trash. You can re-add it as a linked file if you want, but it won't work as a stored file if you're using syncing.