I took an old tablet with a broken screen and installed LineageOS on it, as my first attempt at rooting a device and trying an open mobile OS. This is a great post giving some of the reasons for doing so and a basic outline of the process:

https://brainbaking.com/post/2021/03/getting-rid-of-tracking-using-lineageos/

For me it went pretty smoothly. The most difficult part was actually getting the back cover off my tablet, which isn't necessary for rooting all devices - I had one of the more challenging ones (Amazon Fire HD 8).

I get the impression that privacy is a big motivation for people to switch to open source these days. There are different reasons people care about privacy or sound alarms about privacy violations: for me, it's not so much that I don't want people to know things about me, it's that I don't consent to the economic model of companies tracking me and storing data about me for advertising purposes. So any time I find a way to be in control of the computers I buy and the data I create, I consider it a win.