Here is a simple script to package your plugins for VST3, AU and AAX on macos

build_macos_installer.sh

#!/bin/bash

# Notes:  
# - Im not confident in bash
# - while it works without any issues for our plugins this was made for internal use only originally and I had to remove some stuff
# - replace `<YOUR_COMPANY>` with your company name
# if there are any requirements missing let me know :)

# Requirements:
# all plugin files and the preset folder need to be in the same folder as this script
# the scripts folder needs to be the cwd
# you need to have pkgbuild installed (comes with xcode)
# your EULA file 
# - is in the same folder as this script
# - is called EULA_TEMPLATE.txt
# if you want to supply presets, copy them into a folder "Presets" in this directory

# Check if the user has provided plugin name and version as arguments
if [ $# -ne 2 ]; then
    echo "Usage: ./script.sh <PluginName> <Version>"
    exit 1
fi

# Define the file names using provided plugin name
PLUGIN_NAME=$1
VERSION=$2
AAX_BUNDLE="${PLUGIN_NAME}.aaxplugin"
VST3_BUNDLE="${PLUGIN_NAME}.vst3"
AU_BUNDLE="${PLUGIN_NAME}.component"

#prepare EULA
EULA_FILE="EULA.txt"
cp "EULA_TEMPLATE.txt" "$EULA_FILE"
# replace <PRODUCT_NAME> with the provided product name
# allows for the same eula to be used for multiple products
sed -i '' "s/<PRODUCT_NAME>/$PLUGIN_NAME/g" "$EULA_FILE"

# Define the package identifiers
AAX_ID="com.<YOURCOMPANY>.aax.pkg"
VST3_ID="com.<YOURCOMPANY>.vst3.pkg"
AU_ID="com.<YOURCOMPANY>.au.pkg"
PRESET_ID="com.<YOURCOMPANY>.presets.pkg"

# Define the output installer name
INSTALLER_NAME="${PLUGIN_NAME}Unsigned.pkg"

# Define the destination directories
AAX_DIR="/Library/Application Support/Avid/Audio/Plug-Ins"
VST3_DIR="/Library/Audio/Plug-Ins/VST3"
AU_DIR="/Library/Audio/Plug-Ins/Components"
cp -rf Presets "${PLUGIN_NAME}"
PRESET_FOLDER="${PLUGIN_NAME}"
PRESET_DIR=/tmp/<YOURCOMPANY>

# Temp directories for pkgbuild
TEMP_AAX_DIR="./temp_aax"
TEMP_VST3_DIR="./temp_vst3"
TEMP_AU_DIR="./temp_au"
TEMP_PRESET_DIR="./temp_preset"

# Define the choices-outline part of distribution.xml
CHOICES_OUTLINE="<choices-outline>"

# Create the packages
if [ -d "$AAX_BUNDLE" ]; then
    mkdir -p "$TEMP_AAX_DIR$AAX_DIR"
    echo "Creating AAX package..."
    cp -R "$AAX_BUNDLE" "$TEMP_AAX_DIR$AAX_DIR"
    pkgbuild --root "$TEMP_AAX_DIR" --identifier "$AAX_ID" --version "$VERSION" "aax.pkg"
    CHOICES_OUTLINE=$CHOICES_OUTLINE'<line choice="aax.pkg"/>'
fi

if [ -d "$VST3_BUNDLE" ]; then
    mkdir -p "$TEMP_VST3_DIR$VST3_DIR"
    echo "Creating VST3 package..."
    cp -R "$VST3_BUNDLE" "$TEMP_VST3_DIR$VST3_DIR"
    pkgbuild --root "$TEMP_VST3_DIR" --identifier "$VST3_ID" --version "$VERSION" "vst3.pkg"
    CHOICES_OUTLINE=$CHOICES_OUTLINE'<line choice="vst3.pkg"/>'
fi

if [ -d "$AU_BUNDLE" ]; then
    mkdir -p "$TEMP_AU_DIR$AU_DIR"
    echo "Creating AU package..."
    cp -R "$AU_BUNDLE" "$TEMP_AU_DIR$AU_DIR"
    pkgbuild --root "$TEMP_AU_DIR" --identifier "$AU_ID" --version "$VERSION" "au.pkg"
    CHOICES_OUTLINE=$CHOICES_OUTLINE'<line choice="au.pkg"/>'
fi

PRESET_CHOICE=""
if [ -d "$PRESET_FOLDER" ]; then
    echo "Creating Preset package..."
    mkdir -p "$TEMP_PRESET_DIR$PRESET_DIR"
    umask 000
    cp -R "$PRESET_FOLDER" "$TEMP_PRESET_DIR$PRESET_DIR"
    #chmod -R a+rw "$TEMP_PRESET_DIR$PRESET_DIR" #new
    pkgbuild --root "$TEMP_PRESET_DIR" --identifier "$PRESET_ID" --version "$VERSION" --scripts ./scripts "presets.pkg"
    CHOICES_OUTLINE=$CHOICES_OUTLINE'<line choice="presets.pkg"/>'
    PRESET_CHOICE='<choice id="presets.pkg" title="Presets">
        <pkg-ref id="'$PRESET_ID'"/>
    </choice>
    <pkg-ref id="'$PRESET_ID'">presets.pkg</pkg-ref>'
fi

CHOICES_OUTLINE=$CHOICES_OUTLINE'</choices-outline>'

# Create the distribution xml file for productbuild
echo '<?xml version="1.0" encoding="utf-8"?>
<installer-gui-script minSpecVersion="1">
    <title>'$PLUGIN_NAME' Installer</title>
    <options customize="always" require-scripts="false"/>
    <welcome string="Welcome to the '$PLUGIN_NAME' Installer!"/>
    <license file="'$EULA_FILE'"/>
    '$CHOICES_OUTLINE'
    <choice id="aax.pkg" title="AAX Plugin">
        <pkg-ref id="'$AAX_ID'"/>
    </choice>
    <choice id="vst3.pkg" title="VST3 Plugin">
        <pkg-ref id="'$VST3_ID'"/>
    </choice>
    <choice id="au.pkg" title="AU Plugin">
        <pkg-ref id="'$AU_ID'"/>
    </choice>
    '$PRESET_CHOICE'
    <pkg-ref id="'$AAX_ID'">aax.pkg</pkg-ref>
    <pkg-ref id="'$VST3_ID'">vst3.pkg</pkg-ref>
    <pkg-ref id="'$AU_ID'">au.pkg</pkg-ref>
</installer-gui-script>' > distribution.xml

# Create the final product
productbuild --distribution "distribution.xml" --package-path ./ --resources ./ "$INSTALLER_NAME"

# Cleanup
rm -rf "aax.pkg" "vst3.pkg" "au.pkg" "presets.pkg" "$TEMP_AAX_DIR" "$TEMP_VST3_DIR" "$TEMP_AU_DIR" "$TEMP_PRESET_DIR" "distribution.xml" "$PRESET_FOLDER" "$EULA_FILE"