“Transfer” is rather a misnomer. In reality, your locally stored data and device setup are merely cloned to the new device. Nothing is moved or removed from the original device.
Apps themselves are not directly transferred between devices. For Apps, the transfer process creates a record of the Apps that are installed on the source iPad - and it is this record of installed Apps that is transferred to the target (new) device. For Apps that are both compatible with the target and remain available for download from the App Store, the corresponding Apps are automatically downloaded and installed from the App Store.
If an older App is not compatible with the target, or has been withdrawn from the App Store, the corresponding App will not be installed; any data or files that are explicitly associated with the in incompatible/unavailable App will not be accessible on the target device. Files that have been synchronised with iCloud or other cloud services, or stored elsewhere, will still be available. It follows that such files can only be accessed by Apps with which they are compatible or can be imported.
Should you need additional help, you might seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page.
Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044