Get value from twig tweak without additional markup
A field formatter stores the field object inside of the render array for reference later, so that you can still access the raw values:

{% set field = drupal_field('field_example', 'block_content', 1) %}
{% set value = field['#items'].0.value %}
{{ value }}


This is the same for all field formatters.



Your approach might also work, if you |render the field first and then apply |striptags:

{{ tab1visibility|render|striptags }}


But not in a consistent way, because it depends on the specific field type and the configured field formatter.