default or selected kernelversion does not have config value CONFIG_APOLLO_ELPLUS.
Result is shown for kernelversion 5.4.123

Apollo 3c505 support


Linux Kernel Configuration
└─>Networking support
└─>Ethernet (10 or 100Mbit)
└─>Apollo 3c505 support
In linux kernel since version 2.6.12  
Say Y or M here if your Apollo has a 3Com 3c505 ISA Ethernet card.
If you don't have one made for Apollos, you can use one from a PC,
except that your Apollo won't be able to boot from it (because the
code in the ROM will be for a PC).