If you have time, an old pc and want a project for the weekend, you can setup a pihole, which is a network-wide adblocker. A.k.a it will block ads on any device that’s connected to your home wifi.

You’re going to need to be more specific. Do you mean ads on websites? If so download a content blocker like Adguard.

Controversial opinion maybe, but: pay for your apps/subscriptions. The makers need to feed their families as well. If you don’t want to pay big corporate, or the app doesn’t offer an ad-free alternative, switch to an indie alternative instead. If you can, pay for a lifetime plan.

If you’re on iOS 14 or higher, you can natively use a service that blocks ads via Encrypted DNS.

Sign up for NextDNS and create an adblocking profile. Then follow the set up instructions.

I usually use Mullvad with ad blocking turned on

Pixel + GrapheneOS

Let’s you just outright firewall apps from the internet, plus opens you up to all the FOSS apps.