Thanks to the ever expanding technological capabilities of Big Tech corporations and Governments, nearly every device you get nowadays comes with undesired terms that compromises a user's Personal freedom. But you can with a bit of tinkering knowledge, make your devices much more private. To properly get rid of trackers, we first need to understand the hierachy of the systems we are using.
These devices are very restricted compared to Desktop/Laptop devices but widely regarded by security experts much safer than Laptops and Desktops. This is due to a couple reasons: (including but not limited to)
Such as Android and IOS permission systems that restrict apps and program from accessing directories and sensors they don't need to access hence complimenting the principle of the least privileged
The general rule of thumb is that the more a device is restricted, the harder it is to get rid of crapware, and nothing can be truer when this is applied to Iphone and Ipad devices. Due to Apple's walled garden not much can be done about these other than replacing your propritery Apps with the few FOSS ones available on the AppStore due to apple chraging devs 100$/year.
The same is NOT true for Android devices which are much more open and you have a wide variety of FOSS forks to choose from that are trustless
An android ROM which is pronounced ultimate for it's security. And can install google services as normal apps in a seperate profile, which is opposed to the usual system app. This is because it is safer this way and much less invasive, but not all apps dependant on Google services appreciate this move.
Only supports Pixel devicesThis ROM has MicroG out of the box that you can use, MicroG is a FOSS replacment for Google services, that is much less invasive. [Probably] Has a much narrower support for apps dependant on google services than Graphene's implemenation.
Less secure than Graphene Also only supports pixel devices with the exception of the xiaomi A2An android ROM that is the Grand father of all of them, before lineage there was cyanogen mod which was it's predecessor. That is why it is called Lineage. It is directly based of AOSP. (android open source project)
Someone probably runs it on their samsung fridge, like it has a lot of OFFICIAL1 build but LOTS of UNOFFICIAL builds.
You should only use FOSS apps (Not that they are all private and secure by default), if you need to use "big brother"/Propritery apps. You can use them in different profiles to limit what they can do and track.
The main solution always is to replace propritery crapware with trusted open source software. The trust here isn't a general adjective to all FOSS projects, you have firefox which is filled with tracking and propritery stuff.
Even if the original FOSS project is safe, the binary it is compiled to run on your device might have compromised code. and unless you check and compile everything yourself, you can never be 100% sure you aren't being spied on.
A solution for this is reproducable builds, you don't need to compile everything when people say that they can compile the same source code and the hashes of their binary matches the official one being disturbuted. But this cannot happen for all project and code compilers.
Now back on topic, System76 and pine64 have been making laptops and desktops and put coreboot on them, which is a FOSS bios. Because your bios knows everything you do, back in the good 'ld days even the Linux kernel didn't care about this simply because it is too autistic.
But now maintainers slowly try to protect the software from compromised hardware. Which is how we should be thinking about every computer with AMD's RealME and and Intel's Managment Engine.
And You can always snip snip cut away the gps chipset, the gyroscope, the wifi chipset, the micophone and the camera.
Then use usb microphone and camera instead of integrated, so you can have a peace of mind when they are disconnected.
For new phones and tablets, the same snipping can be done with respectivly using ethernet dongles and docks.
The bootloader is generally propritery on almost all phones that i know of, but they can't be as invasive as the 2 mentioned above.
[1] https://github.com/LineageOS/charter/blob/master/device-support-requirements.md