Please make ionCube or SourceGuardian available on Magento Cloud for PHP 7.4.
We were trying to resolve this issue with partner commerce support in a ticket 354101, but Naga Harika Yarlagadda said ionCube is not supported for PHP 7.4 on Magento Cloud and recommended to create this feature request.
Jus FYI, ionCube officially supports PHP 7.4, so it seems like it is Magento Cloud not supporting it.