Raspberry PI 3B+
4cpu
1gb ram
32gb sdcard

Install latest version of Raspberry Pi Imager. At this time 1.7.2: https://downloads.raspberrypi.org/imager/imager_1.7.2.exe
OS: Raspberry Pi Os 32 Bits
Configured for Headless

After sshing to the Pi, do a sudo apt update and sudo apt full-upgrade

Follow this guide to install BOX32 (thank you so much @Ayyyy for this software):
https://pimylifeup.com/raspberry-pi-x86/

Setup steamcmd following this guide (just the steamcmd part):
https://pimylifeup.com/raspberry-pi-valheim-server/
(dont forget to login into your steam account while on steam shell)

Install KF1 Server following the guide on its wiki, starting just after steamcmd installation ofc:
https://wiki.tripwireinteractive.com/index.php/Dedicated_Server_%28KillingFloor%29#Linux

cd Into [KF1Server_Installation_Folder]/System and execute the start up command.

./ucc-bin server KF-bioticslab.rom?game=KFmod.KFGameType?VACSecured=true?MaxPlayers=6 -nohomedir

Cross your fingers while the server is starting. Will drop some errors/warnings but nothing to care about. It will just successfully start after a while.

Go to your kf1 game and type in console:

open 12.34.56.78

replacing that fake ip with your Pi's IP and Enjoy :)

Actually it runs pretty fast, never lagged even on last waves and I kept a ping below 20ms having wifi connection with a basic router.

# First Boot
1 sudo apt update
2 sudo apt full-upgrade
3 git clone https://github.com/ptitSeb/box86
5 cd box86/
6 mkdir build
7 cd build
9 cmake .. -DRPI3=1 -DCMAKE_BUILD_TYPE=RelWithDebInfo
16 make -j3
17 sudo make install
18 sudo systemctl restart systemd-binfmt
49 mkdir steamcmd
50 cd steamcmd/
60 curl -sqL "https://steamcdn-a.akamaihd.net/client/installer/steamcmd_linux.tar.gz" | tar zxvf -
# Force Install Dir, Steam Login and KF1 Server Install
65 cd ~/killingfloor/System
70 ./ucc-bin server KF-bioticslab.rom?game=KFmod.KFGameType?VACSecured=true?MaxPlayers=6 -nohomedir
# Enjoy