I’m not sure, it depends on your configuration and blocking list. I don’t use native tracking protection, and my blocklist (oisd) prioritizes functionality over blocking, so in my case everything just works and I don’t have anything special added to my whitelist. I don’t like DNS blocking to be in the way and I also share my configuration with some family members, so that’s why I’ve made this choice, but if you prefer a stricter approach you might have to do some whitelisting.
If the iCloud Private Relay ODoH DNS server is used it will show up as a DNS leak, even if the IP address from its response isn’t used for browsing. For privacy it doesn’t matter, as with ODoH the DNS resolver doesn’t know your IP or identity, the most important thing is whether it will bypass the NextDNS blocklist. In my testing I couldn’t visit any website that was blocked by NextDNS, meaning that the iCloud DNS resolver wasn’t used as the primary DNS resolver, which matches with their documentation (that page 10 that I linked to earlier). Note that Apple will only use a custom DNS resolver if you’re using the native DoH option, so for example the configuration that you can get from https://apple.nextdns.io/.
You can easily test it yourself: block a hostname in NextDNS that you haven’t visited recently (due to cache) and try to visit it in Safari.
I don’t know why Apple still uses the Cloudflare DNS resolver even if it seems to be ignoring its responses. Maybe they use it for some custom metadata that’s sent along with the request which somehow is important for the relay. All I know is that I’ve never seen it bypassing the NextDNS blocklist, which again is exactly how it’s documented by Apple.
So for some reason Apple keeps using their DNS resolver even with a custom DoH resolver configured, but in my testing it didn’t affect the blocking capabilities of NextDNS at all, meaning that the answers from their resolver are just ignored (or used for some other purpose). The way NextDNS knows that you’re using another resolver is by letting the browser resolve some unique hostnames, so that way it will show up even if the answers from that resolver aren’t used. As to why Apple does this I don’t know. In theory it could be the case that Apple just used whichever answer arrives first and that NextDNS just happened to be faster in my testing, but that doesn’t match with how it’s documented in their PDF.
Which one to pick (if you don’t just want to use them at the same time) depends on what your goal is. I use iCloud Private Relay + NextDNS + AdGuard, but nowadays I mainly use another browser with a built-in adblocker, so iCloud Private Relay and AdGuard aren’t used in that case.
I use NextDNS everywhere I can and use a list that prioritizes not breaking anything. It’s a nice backstop. It’s not a replacement for an in-browser adblocker in my opinion, unless you don’t care that it’s less effective.
Contrary to common believe, iCloud Private Relay and NextDNS are compatible and can both be enabled at the same time, see page 10 of https://www.apple.com/icloud/docs/iCloud_Private_Relay_Overview_Dec2021.pdf. When you try to visit a blocked hostname in Safari, you’ll see that it won’t work. This is something that I’ve personally confirmed.
What NextDNS solves and iCloud Private Relay doesn’t, is blocking hostnames system wide, thereby completely blocking some ads and tracking. What iCloud Private Relay solves is hiding your browsing traffic a bit better within your local network and from your ISP, as well as hiding your IP from trackers and hiding your identity from their DNS resolver (not from NextDNS, though).
Some background information why using HTTPS together with encrypted DNS doesn’t fully hide which websites you visit (yet): https://blog.cloudflare.com/announcing-encrypted-client-hello.
If I had to choose, I’d go with NextDNS for system wide blocking and I’d add an adblocker browser extension to block trackers and ads that can’t be blocked with DNS based blocking. But you don’t have to choose and can use both at the same time.
Imagine a system where you are just an end user, one of hundreds or even thousands, and the admin removes an application. I would be furious if the admin would also delete my personal application data from my homedir. There could be important settings in there, that I might want to move to another system, or maybe I’ll install my own flatpak in my homedir and continue to use those settings. There could be stuff in there that’s important and for which no backup exists.
So how would you implement that: would you, while uninstalling a system flatpak, be given the option to only remove your personal files and leave the files in other homedirs intact? Or should it remove the files for all other users too, without their permission? In my opinion the best way is to just leave the files alone. I think it makes sense and I think using a 3rd party app to remove the remnants is fine. It works the same on Windows, MacOS and Linux. Maybe adding something to the OS to detect these files and ask each user independently would be a nice addition, but not as part of the uninstall process of the flatpak.
Host based blocking can never be as complete as blocking inside your browser and there is no way around that. The reason is that host based blocking falls short where tracking content and ads are served from the same hostname as the actual content. Furthermore, some tracking hosts might be whitelisted because just blocking them would break functionality.
I personally use uBlock Origin with ETP at its default setting, which works well for me without breakage, but judging from your post you might be looking for a solution without browser extensions. The ETP tracking protection is supposed to block tracking, sometimes without letting the website know that it’s disabled, by replacing the tracking code with dummy code. On strict mode you run more risk of things breaking, similar to how strict host based blocking breaks some websites.
Telegram’s “privacy” is fully based on people trusting them not to share their data - to which Telegram has full access - with anyone. Well, apart from the optional E2EE “secret chat” option with non-standard encryption methods that can only be used for one on one conversations. If it were an actual privacy app, like Signal, they could’ve cooperated with authorities without giving away chat contents and nobody would’ve been arrested. I’m a Telegram user myself and I from a usability standpoint I really like it, but let’s be realistic here: for data safety I would pick another option.