What should I do if I face the well-known spontaneous reboot problem?

[zentekker]

Zenfone 6, 8GB/256GB, ZS630KL-2A005EU
Latest Patch: WW_17.1810.2009.176 ASUS stock ROM
Bootloader unlocked, Magisk.

Hi all,
I never had spontaneous reboots until about September/October 2020. Now I am also affected by this obviously well-known problem. At least I found several people complaining about the same issue.
I own the phone since February and it worked totally flawlessly before. Bootloader was unlocked since the beginning.
The reboots don't seem to follow any pattern: They can happen while the phone lies alone idle on a desk or while typing something. It also seems not to be related to temperature or load.
Is there a fix other than a hardware fix? I read, the mainboard is faulty. How is the procedure to get this fixed?
Best regards

[zentekker]

As an update: Device is now dead and does not react to any button press no matter how long or in whatever combination. It also doesn't react to plugging a charger in. Totally dead now. Will RMA it.