Looking into the recipe for angstrom-lxde-image (meta-toradex-demos/recipes-images/images/angstrom-lxde-image.bb), there is no Qt included in this image. If you want Qt, you could build an angstrom-lxqt-image which includes Qt5 or angstrom-qt-x11 image which has Qt4. You will find the recipes for these also in the meta-toradex-demos layer. Please keep in mind that Toradex does not maintain BSP2 anymore and also Colibri T20 is almost EOL. Are you also looking into migrating from your Colibri T20 module to a newer module?