Xiaomi claims five years of security updates for upper range models that came out last year. Specifically I am thinking about Xiaomi 13T which a couple of my friends use. Their newer phones no longer allow unlocking the bootloader, though.

I've been using a five year old hand-me-down 9T and it was recently updated to Android 14 with security patch from May this year. (Thanks to Lineage, of course — the official support ended in 2021).