Go to System > About this and check you actually are on the latest version. File caches was brought in around 3.3.1.
Other than that, it could be a permissions issue and you're signed in with a limited user role that hasn't been granted the ACL to manage file caches.
Here's what the screen with File caches on should look like:
Please bear with us during the current global situation. The team all have families and local communities to look after as well as the community here. Responses may be delayed during this time, but rest assured we will get to your query eventually.
After upgrading to Version 3.4.11, I loose previews, thumbnails, and purge cache gives me: 504 Gateway Time-out
How can I purge when I always get timeouts?