Not completely correct…
You can brick your phone as well with locking the bootloader after installing FPOS
@2hz3e
Please have look at this topic and follow-up over there if needed. Important is get unlock ability
And important from your link is this
If you install an OS with an older security patch level than your previous OS, Android’s roll-back protection might brick your device when locking the bootloader! Wait until you get a software update with the same or newer security patch level before locking the bootloader.