As a long time iPhone user, I am new to the world of Android. My threat model is just want to protect my privacy from the corporate giants and and trackers (Ads). From my understanding, custom ROM like Lineage is good with privacy but their security updates are behind. Also most phones are not allowed to lock the boot loader after the root. Is there any security threat for that? So for my threat model, I would like to know your suggestions. If I go with a custom ROM, which one you prefer? Also do you have any suggestions about any phone brand or particular model. One more thing I would like to hear from you is that can I get same level of privacy and security from your non-root guide like a custom ROM?

Thank you for your reply. Which is the best phone to debloat now as per your guide. What is your opinion about both nokia and motorola? I like clean Android interface than cosmetic or modified versions.