What does that do?
I can see it in MIUI 9.6.4.0 also in Cleaner App. Not tried though as I dont know what exactly it does.
By the way, WhatsApp is the leading reasons of Smartphones running out of Storage/Disk space. Many users do not know that WhatsApp stores each Image / Video / GIF in sent folder and that never gets cleaned, even when we delete Files from Gallery.
Sent Images are stored in:
Internal Storage > WhatsApp > Media > WhatsApp Images > Sent
Sent Videos are stored in:
Internal Storage > WhatsApp > Media > WhatsApp Videos > Sent
Sent GIFs are stored in:
Internal Storage > WhatsApp > Media > WhatsApp Animated Gifs > Sent
Once a file is sent, even if we delete it from the above location(s), the recipient will be able to "download" it. Hence, it is necessary to clean up the above folders.
I havent yet come across any App or cleaning tool which cleans ONLY the above folders in WhatsApp app.