Around 3 weeks ago we realized images in our newsletter were not loading when opened in macOS 12 & iOS 15 Mail. When opened in different email apps, and in different versions of macOS/iOS Mail, the images would load with no problem. Switching from hosting the images on our usual, shared, server to hosting in Mailchimp also fixed the issue. The images are inserted in an img element's src attribute.
Unchecking "Block All Remote Content" in Mail's privacy settings did not fix the issue. We've downgraded our TLS to 1.2, as suggested in this thread, but that did not fix the issue.
Below are screenshots of the emails in Mail - not working, Gmail - working.
Image hosted on shared server - https://www.tjcresources.net/images/FINAL_Birthday_email.jpg
Image hosted on Mailchimp - https://mcusercontent.com/ef8c6666869c429f75ebf2f2b/images/1bba5438-ed06-45f9-2a4a-853facde56fe.jpg