OnePlus 8T A15 from e/OS 3.2 A14

All the way you need to reach android 14 that is the final firmware version for this device

The way proposed by Lineage look easier than have to restart from scratch :
reflashing the all firmware, unlocking the bootmoader again, reflashing a custom recovery an finally reflashing /e/.

[HOWTO] Upgrade my /e/OS to major Android version without loosing /data