I use Blokada - but not the latest version since the company switched from the free open-source standalone app paradigm to a cloud-based continual paid subscription model. It seems like Blokada version 4 (obtained either from the company's webpage or F-droid I forget which) blocks a heck of a lot more stuff than version 5 for some reason.

On the other hand, it also noticeably heats up my phone if a not-well-behaved app (examples include Freemium games) continually resubmits queries over & over again every (or even multiple times a) second. You can block every request that it makes... but it can also keep making them so... at some point you may question whether the cost is worth it.

This arguably relates more to "tracking" than actual advertisements, since there can only be a finite number of the latter but the former can happen all day every day even when the app is not running, if it decides to be aggressive about checking in with its home base. These days, even if you do pay for something, your data is STILL the actual "product" that is the reason the company is in business at all to obtain.:-(

RethinkDNS is a great option unless you already have something in place that you want to use as well.

For example, I have a pi-hole and a server that I'd like to use 24/7. There's a few ways to do it, but I'm an idiot and need a simple, hard-to-ruin method. So I use the pi-hole as an exit node with TailScale

My personal favorite is RethinkDNS, which is technically capable of running your favorite VPN provider alongside blocking ads and blocking/logging domains on a per-app basis.

It's a bit frustrating to set up for my taste, but it definitely works. (Kudos to Mozilla for sponsoring their project, BTW.)

NextDNS