Installation via OSGEO4W error: Could not load qgis_app.dll

[cdragoste]

Hello, Using the OSGeo4W installer for installing the qgis-ltr, if I choose the last version (3.34), everything works fine. If I try to install an older ltr (3.28 or 3.16) using this installer, after installing it, QGIS not loads at all. The error: Could not load qgis_app.dll

I was wondering if I can use the installer to install the previews ltr version (as far as it seems that the installer gives me this option)

Anybody had this problem before and can give me a clue? Thank you very much

[jef]

"This installer" as in ​https://download.osgeo.org/osgeo4w/v2/osgeo4w-setup.exe ?

You could find more details about why qgis_app.dll is not loading using the hints in ​QGIS #26891.

[jef]

Sorry, misread the ticket:

Easy downgrades are only possible if the dependencies didn't meanwhile change. Otherwise you also need to downgrade dependencies to the version used for the earlier version. Dependencies are not versioned, so that cannot be done automatically. To make it even harder the required older versions might even not be installable anymore as only the current and the previous (and maybe a test version) are referenced.

But you can try snapshots. See ​https://trac.osgeo.org/osgeo4w/wiki#Olderversionsfromreposnapshots

Lacking a better option, resolving this as "invalid".