I just downloaded the app so I’m asking if I still need to use a VPN for it
Hope this helps
It is not necessary for the app to work, but without it yohr ip will be visible to websites tou are connexting to so if you don’t want that you should use a vpn.
Lets say youre in this situation:
Your isp (internet service provider) will be able to see what sites you visit even with https enabled.
Thay cant see what sites you visit if you use a vpn.
Though tracking companies such as google will sell your data, in other eords what sites you visit. In a nutshell youll be anonymous if you stay away from google and co, use a vpn aswell as an ad/trackerblocker 
You’ve never needed a VPN to use the DuckDuckGo app. It’s the same as any other Web browser.
If you want to hide your IP address from websites, for maximum privacy, I’d suggest using Tor. The EFF has a useful interactive page to see what Tor and HTTPS do to safeguard anonymity and privacy. A VPN is mainly useful for high-bandwidth traffic like video.
Does that mean my wifi router can still keep track of my search history?