Edited MO2 Broker for rockerbacon's script suite so that even if the NXMHandler fails, the download will still proceed. Might be useful for Steam Deck users (or Flatpak Protontricks users in general).

modorganizer2-nxm-broker.sh

#!/usr/bin/env bash

# SUPPLY YOUR PERSONAL NEXUS API KEY HERE (nexus_apikey="yourNexusAPIKeyInsideDoubleQuotes")
nexus_apikey="yourNexusAPIKeyInsideDoubleQuotes"

###    PARSE POSITIONAL ARGS    ###
nxm_link=$1; shift

if [ -z "$nxm_link" ]; then
	zenity --ok-label=Exit --ellipsize --error --text \
		"ERROR: please specify a NXM Link to download"
	exit 1
fi

nexus_game_link=${nxm_link#nxm://}

IFS='/' read -ra ADDR <<< "$nexus_game_link"
nexus_game_id=${ADDR[0]}
nexus_mod_id=${ADDR[2]}
IFS='?' read -r nexus_file_id nexus_query_string <<< "${ADDR[4]}"

nexus_file_id=$((nexus_file_id))

IFS='&' read -r key_pair expires_pair user_id_pair <<< "$nexus_query_string"
IFS='=' read -r _ nexus_key <<< "$key_pair"
IFS='=' read -r _ nexus_expires <<< "$expires_pair"
IFS='=' read -r _ nexus_user_id <<< "$user_id_pair"
nexus_expires=$((nexus_expires))

###    PARSE POSITIONAL ARGS    ###

instance_link="$HOME/.config/modorganizer2/instances/${nexus_game_id:?}"
instance_dir=$(readlink -f  "$instance_link")
if [ ! -d "$instance_dir" ]; then
	[ -L "$instance_link"] && rm "$instance_link"

	zenity --ok-label=Exit --ellipsize --error --text \
		"Could not download file because there is no Mod Organizer 2 instance for '$nexus_game_id'"
	exit 1
fi

instance_dir_windowspath="Z:$(sed 's/\//\\\\/g' <<<$instance_dir)"
pgrep -f "$instance_dir_windowspath\\\\modorganizer2\\\\ModOrganizer.exe"
process_search_status=$?

game_appid=$(cat "$instance_dir/appid.txt")
steam_compat = $HOME/.local/share/Steam/steamapps/compatdata/$game_appid

if [ "$process_search_status" == "0" ]; then
	echo "INFO: sending download '$nxm_link' to running Mod Organizer 2 instance"
	download_start_output=$(WINEESYNC=1 WINEFSYNC=1 protontricks-launch --appid "$game_appid" "$instance_dir/modorganizer2/nxmhandler.exe" "$nxm_link")
	download_start_status=$?

	if [ "$download_start_status" != "0" ]; then
		api_url=$"https://api.nexusmods.com/v1/games/${nexus_game_id}/mods/${nexus_mod_id}/files/${nexus_file_id}/download_link.json?key=${nexus_key}&expires=${nexus_expires}"

		nexus_response=$(curl -X 'GET' \
  					 "$api_url"\
  					-H 'accept: application/json' \
  					-H "apikey: ${nexus_apikey}")

		uri=$(echo "$nexus_response" | python3 -c "import sys, json; data=json.load(sys.stdin); key='URI'; print(data[0][key] if isinstance(data, list) and data and key in data[0] else 'Unexpected structure or key not found')")

		filename=$(basename "$uri")
		filename=$(echo "$filename" | sed 's/\?.*$//')
		uri_link=$(echo "$uri" |sed -e 's/ /%20/g')

		download_start_output=$(curl -C - -L "$uri_link" -o "$instance_dir/modorganizer2/downloads/$filename" 2>&1 | stdbuf -oL tr '\r' '\n' | \
			stdbuf -oL awk '/%/ {gsub(/%/,""); print $1}' | \
			while read -r progress; do
			    echo "$progress"
			done
			) |
		zenity --progress \
		  --title="Downloading Mod" \
		  --text="Downloading $filename..." \
		  --percentage=0 \
		  --auto-close \
		  --auto-kill

		download_start_status=$?
	fi

else
	echo "INFO: starting Mod Organizer 2 to download '$nxm_link'"
	download_start_output=$(steam -applaunch "$game_appid" "$nxm_link")
	download_start_status=$?
fi

if [ "$download_start_status" != "0" ]; then
	zenity --ok-label=Exit --ellipsize --error --text \
		"Failed to start download:\n\n$filename"
	exit 1
fi