How to add multiple performers to event schema with seomatic
I hadn't seen those examples but it is bookmarked now.

I've adapted your example as below and it's all working. Thanks @andrew.welch

{% set performersArray = [] %}
{% for block in entry.performers .all() %}
  {% set performersArray = performersArray | merge([seomatic.jsonLd.create({
      'type': block.performerType,
      'name': block.performerName,
  }, false)]) %}
{% endfor %}
{% do mainEntity.performer(performersArray) %}