Based on your description, I understand that the external users cannot download the shared files, but they can edit files without any issue.
First of all, I want to know the following information at your convenience.
- When you share files with external users, through Anyone with the link or Specific people?
- When external users cannot download shared files, do they receive any error messages?
In addition, please also try out the following methods and let me know the result.
- Let users to switch to different browser to download shared files.
- For the shared files, go to File -> Save as -> Download a Copy to download, check whether they are able to achieve this.
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.