Yes it is still under warranty. I mentioned earlier that there is no advanced bios option for this laptop model (Lenovo Legion Pro 7i). When I flashed an older version of BIOS from Windows, the GPU worked fine again, until the fourth restart. I thought that a Windows update was the problem which installed the Intel graphics driver but now when I uninstalled that as eidariaman1 suggested eralier, the problem is still there. I made a video proof and will contact Lenovo support.
My concern is, that this exact same thing happened with my previous original motherboard, and now this is happening on my new replaced one as well.