Lenovo Problem

Trying to help a friend who bought a supposedly new Lenovo V15 G2 IJL that is not under warranty. problem is that it takes over 10 minutes to start up. 10 minutes of black screen. White power light is on immediately but black screen for 10 minutes. Once it does boot it runs fine for a half hour or so before locking up. Acts same with or without charger plugged in. So far I have:

Updated bios

Clean install of windows

Tried a different m2 drive

Installed vantage and hardware tests all say ok

monitored temps with core temp seems ok

Shall I assume motherboard problem not worth fixing? Thanks for input