Any mechanical concerns with this design? Seller thinks it folds but it looks like it separates to me.

Hard to tell the model from that one image, but it looks like an early to mid 70’s DA40E, and yes it is a break apart frame, but still considered a “folder.”

If it is a DA40E then it should have 20×1.75 tires, this is only relevant because some Peugeot folders (UNS40 etc…) had 22×1 3/8 tires and can be a bit hard to find. Early production DA40E’s often came with single speed coaster hubs, while most of the later units came with Torpedo 2spd Duomatic or Automatic hubs.

Cool little bikes, but French threading and cottered cranks are archaic and can be a pain to work with.