CONFIG_INTEL_TDX_GUEST is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT

Intel TDX (Trust Domain Extensions) - Guest Support

configname: CONFIG_INTEL_TDX_GUEST

Linux Kernel Configuration
└─>Processor type and features
└─>Linux guest support
└─>Intel TDX (Trust Domain Extensions) - Guest Support
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
Support running as a guest under Intel TDX. Without this support,
the guest kernel can not boot or run under TDX.
TDX includes memory encryption and integrity capabilities
which protect the confidentiality and integrity of guest
memory contents and CPU state. TDX guests are protected from
some attacks from the VMM.