The tracking, the data mining, the privacy invasions...all can be addressed successfully, although it takes a lot of configuration and a fair amount of knowledge. My 6 year old Galaxy S5, running Lineage OS, does have google stuff on it...because the company I work with uses google tools so I have to have access.
To deal with this, I have three different firewall profiles. One profile blocks everything google from the internet. The second profile - the one I use most of the time - allows enough google traffic for the Hangouts app and the Meet app to work, because I need those for my work. The third profile allows a lot more google traffic, for those occasions (mostly when I am overseas or when I am doing updates from the play store) when I don't mind the tracking and need location-related services to navigate in these foreign lands.
In my day to day use, my phone does not spy on me. I do access FB and some other social media sites using my phone, but I never use their dedicated apps; they DO spy and you can't stop them. I just use a browser. Usually Brave, which works just fine.
Now, the point about a built-in battery is well-taken. I presently have started to shop for a new phone; mine is getting a bit twitchy due to its advancing age, and at this point I have not identified any phone that both has a removable battery and is supported by Lineage OS. I am thinking maybe the FairPhone 3 will become supported, but so far it is not.
I recently purchased a smart TV that runs android. Can't root it...won't let it spy...so I have to reorganize my network. I deployed a vlan (which I call the IOT vlan) just for the TV. I then deployed 2 raspberry pi computers (both running raspberry pi OS on arm processors, btw). One RPI has become a pihole DNS server for my entire network. It resides on both the main LAN and the IOT VLAN, and provides ad- and tracker- blocking DNS to every one of my devices and VMs. On the IOT VLAN, it is firewalled off completely except for port 53, thus permitting the TV to use it for DNS but not to have any access to it other than DNS.
The other pi has been configured to reside completely on the IOT VLAN, with no connection to the main LAN, and to function as a filtering VPN gateway/proxy for the IOT VLAN.
This VLAN is firewalled off at the router so that no internet traffic to or from it is allowed, except for traffic from this raspberry pi. Naturally, the router also denies traffic between LAN/VLANs; the whole point is to prevent this. Thus, the IOT VLAN is fully isolated from my other systems and traffic, and its DNS comes from a device that filters and its gateway also filters as well as conceals my location.
The TV is told to use the RPI as its gateway. The RPI receives traffic from the VLAN, filters it to remove any packets that have a destination that is identified as a DNS server (thus filtering out DoH and DoT traffic), then sends the traffic out a VPN.
I confess that my main NAS also resides on the IOT VLAN (as well as another vlan and the main lan) with one SMB share exposed (named Videos). and devices on the IOT vlan have access to this share as read-only guests. This NAS is quite secure, though, and I don't anticipate any malware on the TV being able to break into it.
I have been monitoring the TV since I set it up (about 3 weeks ago) and I have all tracking blocked. I do have to allow a bit of it for certain content to work, but it is a tradeoff I can choose to make or not, and the security means that my location is anonymous and no other systems that I own and use are being identified and targeted.
As for a portable roll-your-own device that can access the cell network, take a look at
https://www.quectel.com. I am presently evaluating and using several different models of their pcie LTE modems, and I must say I am quite impressed. If you were to purchase one of these (I presently am looking at the EC-25AF and EC-25AFX, and have previously evaluated the EP-06, and I can recommend any of them, depending on your particular needs) and install it in a pcie to USB adapter that will handle a SIM card (like this
https://www.amazon.com/Adapter-Express- ... 284&sr=8-4), you could plug it into a USB port on the RPI and you would have your cellular connection. There is driver support for Linux; it would be no problem to get it going and to configure it for data. I am in fact doing that using freebsd as my OS for some work I'm doing. For FreeBSD, I have had to do some driver work, but these modems are working well. I have not investigated how to configure it for voice, but I am sure there is software available.
The point is that you can indeed preserve your privacy and stop the spying. It isn't easy, but it can be done.
Here is the code I wrote to block DoH traffic. I just run it at the end of my normal firewall script.
https://github.com/jiml8/blockDoH/blob/ ... lockDoh.py