GoogleMaps plugin marker setOptions error
Icon management is handled a bit differently in the new Google Maps plugin. Now, you set icons before the map is rendered, even in Twig!

Official guide for Setting Marker Icons

{# Get all bars &amp; restaurants #}
{% set bars        = craft.entries.section('locations').type('bars').all() %}
{% set restaurants = craft.entries.section('locations').type('restaurants').all() %}

{# Create a dynamic map (with no markers) #}
{% set map = googleMaps.map() %}

{# Add all bar markers #}
{% do map.markers(bars, {
    'icon': '/images/bar-icon.png'
}) %}

{# Add all restaurant markers #}
{% do map.markers(restaurants, {
    'icon': '/images/restaurant-icon.png'
}) %}

{# Display map #}
{{ map.tag() }}