No, when you use a VPN, your ISP won’t be able to tell what you download online. In fact, due to strong encryption and tunneling, your internet service provider and anyone other than your VPN provider won’t able to determine your online activities.
Since a VPN handles all of your network requests including routing and DNS resolution, everything you do online remains discrete. Top tier VPNs offer a variety of encrypted protocol like IKEv2 and OpenVPN to establish secure end to end connections.
That said, it is possible for your ISP to know whether or not you’re using a VPN. That’s because ISPs can identify servers that are owned by VPN providers. However, as I mentioned earlier, your ISP wouldn’t be able to determine your browsing activities. Even more amazing is the fact that some providers offer obfuscation technology that can disguise your VPN traffic to appear as ordinary HTTPS traffic.