FAPI #prefix YAML filter tag
You need to include the #allowed_tags property which is applied to #markup, #prefix, and #suffix. (See: Pass raw html to #markup)

button_submit:
  '#prefix': '&lt;div class="col-md-4 text-right"&gt;text&lt;button&gt;button text&lt;/button&gt;'
  '#suffix': '&lt;/div&gt;'
  '#value': Send
  '#type': submit
  '#allowed_tags':
    - div
    - button