Oneplus is dead for me since der Switched their underlying OS to ColorOS. On month after the update my device bootloped and the only option was to wipe all the data. I don’t rooted the device everything was stock. Second thing is I got only 2 mayor Android updates on my Oneplus Nord.
https://support.fairphone.com/hc/en-us/articles/18682800465169-Fairphone-5-OS-Release-Notes
So far, security updates have been delivered after 1 Month. Security updates can also be delivered after the release of a new Android version.