When you move a folder in macOS and a folder with the same name exists in the destination, Finder asks if you want to overwrite the destination. Be warned: “overwrite” means replacing the destination folder without any way to undo it. Make sure you have a Time Machine backup ready.
I find it perplexing that hard deletion of the destination is the default action, and you must press Option while moving the folder to merge.
Yes, this matches file behavior — but it feels like UX sacrificed for the sake of consistency.