A logic issue was addressed with improved checks. This issue is fixed in iOS 18.7.5 and iPadOS 18.7.5, macOS Sequoia 15.7.4, macOS Sonoma 14.8.4, macOS Tahoe 26.3. Turning off "Load remote content in messages” may not apply to all mail previews.
https://support.apple.com/en-us/126350
https://support.apple.com/en-us/126349