CONFIG_ARCH_IXDP2801 is not available for thedefaultarchitecture x86.
Result is shown for architecture arm
default or selected kernelversion does not have config value CONFIG_ARCH_IXDP2801.
Result is shown for kernelversion 6.2.5

Support Intel IXDP2801 and IXDP28x5

configname: CONFIG_ARCH_IXDP2801

Linux Kernel Configuration
└─>Intel IXP2400/2800 Implementation Options
└─>Support Intel IXDP2801 and IXDP28x5
In linux kernel since version 2.6.12  
Say 'Y' here if you want your kernel to support the Intel
IXDP2801/2805/2855 reference platforms. For more information on
this platform, see Documentation/arm/IXP2000.