Fence guys don’t know retaining walls.
The tallest part of the wall needs redone. It may last a year or more so there’s time.
Wood lasted nearly 40 years in the same site, so treated wood sounds like the obvious choice.
The fence guys didn’t put in any drainage and that may be contributing to the bowing we see.
An idea gallery … U like 3rd in on the top row. Nice simple – clean.