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?
If you use https then your isp can only see the domain (ie. duckduckgo.com) but not the specific page you’re viewing. So they may know you watch pornhub but they can’t know what vids you’re watching.
If you use VPN you hide that from your isp but you share the data with your VPN provider, so you’re not safer by any means.
Unless you have a reason to believe that the VPN is more trustworthy
Yea but problem is on phones mainly captchas don’t work for tor
Someone said this a few months back, I don’t know why people think this but your router doesn’t keep track of your search history.
Your ISP on the other hand may do, and probably does. A VPN is to stop that, but you’re trusting in the VPN company to delete logs instead.
yes, but you can change your dns address this way hidding your traffic from your isp(internet service provider)