Combining two field options

Is it possible to combine two managed metadata fields together?
'UsersA' is a taxonomy field and 'UsersB' is a folksonomy field. I would like to present all the tags associated with each term set into one field for users to choose from. However, if an option is not available then the user selects the "Not Available" which is listed in "UserA' term set. Another text field ('UsersC') should then appear which would allow users to type a custom term. Any guidance is highly appreciated.

Hello @MRizz226,

Welcome to Plumsail Community!

You can see this post for more information or address your question to Microsoft community.

Regarding hiding field dynamically, you can use this code to show/hide field depending on Managed Metadata field value:

function showHideField() {
	if (fd.field('TaxonomySingle').value.name === 'Some value') {
		// Show field
		fd.field('Field1').hidden = false;
	} else {
		// Hide field
		fd.field('Field1').hidden = true;
	}
}
fd.field('TaxonomySingle').ready(function(field) {
	// Calling showHideField when the value changes
	fd.field('TaxonomySingle').$on('change', showHideField);
	// Calling showHideField on form loading
	showHideField();
});

Learn more in Work with SharePoint form fields in JavaScript article.