Proton script to run non-Steam Apps on Linux. Supposedly you have to install Steam first (requires Steam account). Then put this to `/usr/bin/proton.sh` and add required file permissions.

proton.sh

#!/bin/bash

# Credits: https://pastebin.com/NJxfe8Ex

PROTON_VERSION="5.0"
PROTON_DIR=$HOME/.steam/steam/steamapps/common/Proton\ $PROTON_VERSION
RUNNING="$1"

if [ ! -f "$PROTON_DIR/proton" ] ; then
    echo "Proton version $PROTON_VERSION not found!";
    exit
fi

if [ ! -f "$RUNNING" ] ; then
    echo "$RUNNING does not exist!";
    exit
fi

printf "Proton (\033[32m$PROTON_VERSION\033[0m) script found at\n  \033[32m$PROTON_DIR/proton\033[0m\n\n"
printf "Now running\n  \033[32m$PWD/$RUNNING\033[0m\n"

export STEAM_COMPAT_DATA_PATH="$HOME/.steam/steam/steamapps/compatdata"
export MOUNT_PATH="/mnt/c"

PROTON_USE_WINED3D11=1 \
#PROTON_NO_D3D11=0 \
PROTON_NO_ESYNC=1 \
$HOME/.steam/steam/steamapps/common/Proton\ $PROTON_VERSION/proton \
run $RUNNING \
&> /dev/null

exit 0

Ah, so it looks like Proton automatically gives a unix prefix to each game. Fair enough.