How to move a folder to another path and to move back to same tree merging its contents on Unix?

On my Android phone, I have:

• A cron job to move files at 1:59am from /sdcard/WhatsApp/Media to /sdcard/wppmediabkp folder before WhatsApp backup at 2:00am:

mv -f /sdcard/WhatsApp/Media /sdcard/wppmediabkp

• A cron job to move files at 2:30am back (from /sdcard/wppmediabkp to /sdcard/WhatsApp/Media):

mv -f /sdcard/wppmediabkp /sdcard/WhatsApp/Media

• The "cron jobs" are tasks on "Tasks!" app (scheduling them with 00 59 1 ? * * and 00 30 2 ? * *). The commands are tested in Termux app also.

Aim:

• To exclude Media folder from backup, but to also restore image "link" to chats (to do not download again).

On restoration of wppmediabkp folder to /sdcard/WhatsApp/Media:

1. Sometimes it works well (it creates the /sdcard/WhatsApp/Media with all its contents). It happens when /sdcard/WhatsApp/Media folder does not exist. For me, it is the expected behavior.


2. Sometimes it creates a subfolder (/sdcard/WhatsApp/Media/wppmediabkp). It happens when /sdcard/WhatsApp/Media folder exists. For me, it is the issue - I would like to restore original folder tree, merging its contents.

I think it was reduced to a Unix issue, because I can use all Unix basic commands.

How to solve it (to get Media folder back merging its contents) using mv command?