I have the same problem. I've noticed it's emails with attachments. Since the most recent update, Thunderbird doesn't load the email when clicking on the entry in the inbox, and then when double clicking to open in a new tab, the main window is blank with a Loading... text on the top left, and the URL shown above starts with chrome://

Try to rebuild the index file of the troubled folder.

Right-click the folder - Properties - Repair Folder

Sorry, doesn't work. Bo

What is your anti-virus software?

Try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder

It's not just one folder, it's all folders for all accounts. Repairing the folders doesn't seem to change anything. I don't have any special antivirus, I just use Windows Defender.

Iker,

please start a new topic for your problem. https://support.mozilla.org/questions/new

I have Advance System Care, which includes a virus protection agent. Bo

You have marked this topic as 'Solved'. Is it?

If not, try to start Windows 11 in safe mode with networking enabled.

Then tray again to rebuild the index file of the troubled folder.

Does the problem go away?

Windows safe mode disables anti-virus software. This is a troubleshooting step, not a solution.

I have found a temporary solution to reading the mails (but not rectifying the problem): right click the mail heading. Select "Open" and select "Open in new window". Bo

What are you doing differently when the message contents is not displayed?

I don't do anything differently. Pointing to the message heading normally displays the content in the pre-view window, or double clicking on it opens the mail. Both these actions still work for messages without attachments, but none of them for mails with attachments. Bo

Such issues usually happen due to display or rendering problems in Thunderbird, especially on Windows 11. Try switching View → Message Body As → Plain Text, disabling hardware acceleration in Settings → General → Performance, and restarting Thunderbird. Also check whether remote content is blocked in those emails and repair the folder by right-clicking it → Properties → Repair Folder. Updating Thunderbird is also a common solution for such problems.