Cannot Open Zipfile Created By Thunderbird Email

On computer #1 I created a backup to a zip file of my Thunderbird email profile. To do this I used TB's Tools>Export function. When I open the resulting zip file (Thunderbird_profile_backup 20230626) I can see its contents.

Then I did exactly the same thing on computer #2. When I try to open that zip file I get an error message stating it's not a valid zip file.

The sizes of each zip file is around half a gigabyte. Both computers will open other zip files. Both computers are running Windows 10 and both have the same version of Thunderbird and Firefox.

Can somebody please let me know how I can open the zip file created by computer #2?

NOTE: This is related to a different problem that I have with computer #2 (Using TB, I cannot send emails but I can receive them).

 

I haven't used Thunderbird in a while but see if this helps.
https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird