We currently have no way to specify the minimal glibc version needed.
But we recommend to build AppImages on no newer distribution than the oldest still-supported LTS release of Ubuntu. This is also the requirement to be listed on AppImageHub.
Tools like go-appimage and GitHub - AppImageCrafters/appimage-builder: GNU/Linux packaging solution using the AppImage format can bundle everything in the AppImage, including glibc, and hence can produce AppImages that can run even on older systems than the one used for compiling.