The design of the AT-AT is not the same as the ones seen in The Empire Strikes Back, but rather a hybrid of early illustrations for the vehicle by Ralph McQuarrie and Joe Johnston.
The interior of the Clone's AT-TE has a decal for Coruscant's Clone nightclub '79s' seen in the Clone Wars episode Orders (2014) and a pin-up of Senator Padmé Amidala that was used as Gunship cone nose art seen in the unfinished episode A Distant Echo (2020).
The design of the Fifth Brother Inquisitor was inspired by unused artwork generated for Star Wars: Episode VII - The Force Awakens (2015) by concept artist Christian Alzmann. The book "The Art of Star Wars The Force Awakens" reveals it was Alzmann's first attempt at drawing a new 'Sith' villain at the very start of the concept phase began at Lucasfilm in early 2013, when the script was still in the first stages of development.
The Clone Troopers' AT-TE seems inspired visually by Howl's Moving Castle. From the way it walks to the chimney puffing out smoke from the side, like it is powered by a steam engine.
First appearance of the Fifth Brother.