Since you are on 10.5.2, are you running Time Machine? If so, that's the easiest way. Just open Finder to Applications > Graphisoft > ArchiCAD 11 > ArchiCAD Library 11 and then enter Time Machine. Move backwards in time until you see the Texture folders etc shown, select them, and click Restore.
Otherwise, I think you'll have to reinstall 11 from the DVD and then apply the updates again.
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB