Please understand a substantial amount of fixes are only available via the Pixel Security Bulletin which is only made available for the latest branch of Android. ie.:
- the latest PSB for A15 is November 2024
- the latest PSB for A14 is October 2024
- latest for A13 is September 2023. As in FP4 on stock is missing 14+ months of security fixes.
I explained this here: Pixel vs. Android security bulletin