Browers work for you, not apps
Anti-circumvention laws prohibit the circumvention of technological barriers for using a digital good in certain ways which the rightsholders do not wish to allow.
https://en.wikipedia.org/wiki/Anti-circumvention_laws
It is this reason that most tech companies urge you to use their app. Whether it's a supermarket, food service or online second-hand marketplaces. When you navigate an app, you must abide by the rules of the apps' walled garden. Within these walls you have little say how things are run.
You'll never see an ad-blocker for an app, because this would go against anti-circumvention law. It is completely feasible for these to exist, technically, but few developers were dare to have their name associated with something that can carry heavy penalties & fines.
Web Browsers are different. Another term for a browser is a User Agent. These agents work for you, the user. Since the job of a browser is to fetch the content on the web you requested, & then do the job of displaying that content once it reaches your machine, they do not apply the same restrictions as apps.
You can install an ad-blocker on a browser as it does not bypass an access-control in someone else's system. The ad-blocker filters out what you don't want (from the response you got back) rather than preventing the site you visited from ever returning that content in the first place.
When my partner & I order food to be delivered, if the bag the food comes in contains leaflets we don't want, I might discard them before my partner has to see them; I know she just wants the food we ordered, with no junk in the way. In doing this I've not impeded the restaurant in their operation, I've just acted as a filter.
Browsers can be configured in amazing ways. I use the Unhook (https://unhook.app/) extension so that when I visit YouTube, I'm not distracted by suggested videos & instead only see what I'm subscribed to. ClearURLs (https://docs.clearurls.xyz/1.27.3/) removes tracking from URLs, meaning I can easily share a web link that's as short as possible & without passing on tracking info.
The law prevents the same being done to the apps on your phone.