diff -rupN --no-dereference qgis-3.18.1/src/core/qgsapplication.cpp qgis-3.18.1-new/src/core/qgsapplication.cpp

--- qgis-3.18.1/src/core/qgsapplication.cpp	2021-03-19 13:09:08.000000000 +0100

+++ qgis-3.18.1-new/src/core/qgsapplication.cpp	2021-03-24 00:58:46.103156947 +0100

@@ -311,6 +311,11 @@ void QgsApplication::init( QString profi

         {

           myDir.cdUp();

         }

+        // Fix for server which is one level deeper in /usr/libexec/qgis

+        else if ( applicationDirPath().contains( QStringLiteral( "libexec/qgis" ) ) )

+        {

+          myDir.cdUp();

+        }

         myDir.cdUp(); // Go from /usr/bin or /usr/lib (for server) to /usr

         QString myPrefix = myDir.absolutePath();

         setPrefixPath( myPrefix, true );