When you set
[post taxonomy] [is equal to] [my_choice]
You are using the built in Taxonomy in WP.
is not an ACF Taxonomy field.
The taxonomy field in ACF is not a choice field like a radio, checkbox or select. When you create a choice type field you specify what the values will be.
When I want to create a field where the user can select something and that selection will be used as a condition on another field I use a standard select field, dynamically populated it, as in the code I gave previously, and then when the post is saved I do all the work myself of setting the taxonomy either with a acf/save_post or acf/pre_save_post filter.
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