When do we use 'will be' + v3 form of verb? Example, 'I will be finished in an hr vs I will have finished in an hr.' What is the difference?
In I will be finished, "finished" isn't functioning as a past participle, but as an adjective, meaning "complete, done".
In a different tense, it is "I'm finished".
As Tim Baverstock points out, it could in principle be passive "I will be finished" = "Something will finish me"; but this use is rare with an person as the subject. "The work will be finished" is more natural as a passive.