In the last update of Outlook on Windows, Microsoft introduced a bug: when you write an email, images are broken in your signature.
The Microsoft team is aware of the bug and they are working on a fix.
While we wait for a long-term fix, they advised us to downgrade the Outlook version.
To downgrade your Outlook version, you can follow those steps:
1. Got to admin.microsoft.com.
2. In the sidebar, click on Settings and then on Org settings
3. In the list, search for Office installation options and click on it.
4. In the opened page, select the "Every six months" option and click save.
It can take up to 24 hours to reflect on your co-workers Outlook.