DNS blocking with tools like DNSNet get you halfway there without tampering with the apps. It installs itself like a VPN and filters dns requests to ad domains using lists from the same sources as the adblockers.
I say halfway because some apps have a fallback, built-in, ad when it can't reach the server, other serve the ads from their own servers so no way to block them. Most only leave a blank space.
On Android there's also "Private DNS" where you can set a different server to resolve domain names. This way, you won't need to install and run additional apps and can still use VPN for ... well VPN.
I say halfway because some apps have a fallback, built-in, ad when it can't reach the server, other serve the ads from their own servers so no way to block them. Most only leave a blank space.