Does OST LA work on lock bootloader? I tried on my locked bootloader it just stuck on reflash service bootloader.

Hi I have Nokia 7 Plus stuckbin bootloop and bootloader is locked. I was on April 2020 security patch. Then found some online service guy he downgrade to 8.1.0 firmware 213b something via online service tool 6.3.5 but phone is still bootloop. Just wondering can we revive this phone? Please help. Thanks