There are instructions for doing this on almost every brand of phone out there, but some are much easier than others. If you're a beginner at this, I would suggest the Google Pixel 4A or the Samsung Galaxy S 21. Mine is a Google Pixel 5. Generally what does all the snooping is not the base operating system, but all the added bloatware the cellular carriers add to it. So step one is to unlock and root the phone. My phone was rooted before it was even allowed to connect to a network.
Step 2 is to install the OS you want, based on your needs and wants. I lean towards privacy and security, and there are multiple ROMs you can install on your phone that accomplish that. GrapheneOS, CalyxOS, CopperheadOS, and LineageOS are prime examples. I use LineageOS, which is a base Android installation with no ties to Google at all. The Google Play Store isn't even installed by default. So, if you want to download apps, you'll have to install an app repository to do it. MicroG is an option that will give you some access to Google Play apps without actually having to install Google Play. However, having Google Play installed on your phone is okay as long as you keep a leash on it to prevent it from phoning home so much.
For that I use a few different security apps and a firewall. I recommend Quantum Flare, which provides full control over which apps have access to the internet and which don't. You can even give partial access to apps, allowing them to connect to one server but not others. Problem is, this is where you're going to start needing to understand basic networking, IP addresses, and network ports to create solid firewall rules.
Oh, and you will void your phone's warranty the minute you root it, so if you do it incorrectly and brick the phone, they're not going to exchange it. So a solid grasp of basic technical knowledge is highly suggested for anyone attempting to do this.
My advice is, if you didn't understand what I said about firewall rules, IP addresses, and network ports, you should pay a friend $50 to do the rooting process and ROM installation for you, then install whatever you want once that's done.
Let me know how it goes.