In the entity you are using, add a boolean attribute called EnableButton.
Create a microflow that checks the value entered in the textbox and determines if the button should be enabled or disabled. Set the EnableButton attribute accordingly.
Select your new microflow as the OnChange microflow for your text box.
Finally, make the button Enabled based on the EnableButton attribute.
Or to avoid adding extra boolean attributes, in the microflow on your button, check the text attribute value and either perform the action or exit based on the value. The button will still be enabled, but will do nothing ir it fails the check.