Yes, it's feasible to operate a TF2 server on Raspberry Pi 4.
Yes, it's feasible to operate a TF2 server on Raspberry Pi 4.
It's actually achievable using emulation (X86Box), but the server will technically perform poorly. A leaked version of the GoldSRC (HL1, CS, TF1, etc.) binary exists for ARM and could be compiled to run there. It's unclear what it is or where you can obtain it.