(IMHO) CalyxOS is a good balance between security and usability. Better than LineageOS, worse than GrapheneOS (and DivestOS).

Those conspiracy theories often come up in discussions here on Lemmy, but the TLDR is: Google is a tiny player in the smartphone market, compared to vendors like Apple, Samsung, Huawei, Xiaomi, and others (https://www.statista.com/chart/25463/popularity-of-google-smartphones/). They also serve a much smaller geographical region than most other manufacturers. The Pixel 9 lineup, for example, is only sold in 32 countries. Most of those are wealthy industrial nations. Google doesn’t even try to assume market share in developing countries in Africa and Asia. It can also be assumed that over 97% of Google Pixel users keep the Stock Pixel OS, where Google doesn’t need a hardware backdoor since they can just implement it in software. So that leaves only a tiny fraction of all users: people in some wealthy industrial nation who specifically buy a Pixel to install a custom ROM. GrapheneOS for example has about 300K users. Do you really think Google would put in the effort to create a hardware backdoor and take all the risk associated with it (negative PR, loss of sales, etc.) just to collect some data about this tiny amount of users? Google already controls EVERY Android phone on the market by forcing vendors to include Google Play Services as a system application through their contracts, licensing and monopolistic market position. Be realistic for a second, and you will realize that your backdoor theories make absolutely no sense and that no business in the world would ever take such a huge risk with such little reward.