ImportExport NG is listing an old version
This only affects ATN being opened via Firefox. If I search for ImportExport NG, it only lists version 14.1.10, which is compatible with 128.0 - 140.*.
The most recent version however is 14.1.14, which is compatible with 140.0 - 144.*
If ATN is supposed to show the version for the current ESR (140.0) it should show 14.1.14
Apparently this only affects mail extension experiments, and not (API) web extensions
From what we see we can force visibility of the latest version 14.1.14 by setting its strict_min_ver to 136 on ATN, which does not make sense. Versions that have any higher minimum version number will not be shown on ATN. I suspect this will also affect any Add-on that has minimum version set to the current ESR, 140.*.
After the server was restarted today, the current data from http://product-details.mozilla.org/ is used, and ATN shows the correct versions now.
To fix this issue permanently, the cached data has to be updated periodically, or the server has to be restarted periodically.