Administrator-Approved InfoPath Form Fails to Upload After Upgrade to Subscription Edition

The key issue is the current support boundary, not the binding redirect. Microsoft’s lifecycle documentation states that InfoPath Forms Services in SharePoint Server Subscription Edition was supported only until July 14, 2026; it is now unsupported. Consequently, there is no Microsoft-supported way to restore an administrator-approved, browser-enabled managed-code form by installing Office assemblies, copying DLLs into the GAC, or redirecting Microsoft.Office.InfoPath versions. The validation error is consistent with the required server runtime no longer being present or supported. Remove the Central Administration web.config change and avoid altering farm binaries. Preserve the original XSN, source code, data connections, and a functional export from the 2019 environment for analysis, but do not treat an unsupported legacy farm as the production solution. Inventory every rule, connection, code path, permission, and submission target, then rebuild the form on a supported platform. Microsoft recommends evaluating Power Apps; complex server-side logic may require a supported service.