Is the verb in this sentence an action verb or linking verb Susan appeared confident during the debate?

The verb 'appeared' is both a linking verb and an action verb.

The easy way to recognize a linking verb is that a linking verb acts as an equals sign, the object of the verb is a different form of the subject (Mary is my sister. Mary=sister); or the subject becomes the object (My feet got wet. feet->wet); for example:

Susan appeared confident during the debate. (Susan->confident)

The verb 'appeared' is an action verb because it is a Word for the 'act of' appearing. Appeared is not always a linking verb but appeared is always an action verb. Another example:

Susan appeared out of nowhere. (appeared is not a linking verb; 'out of nowhere' is not Susan or a form of Susan)
Linking Verb
Yes, 'appeared' is used as a linking verb. (Susan -> confident)