You must RMA the card and when you get your new one, please have the following in mind.
This is not Blizzard’s fault.
I have a Gigabyte RTX 3080 Ti as well and at least in my case the issue was caused because my card’s failsafe for temps built in Gigabyte’s bios didn’t work as it should, resulting in the card overheating.
Thankfully, my card didn’t die.
It would have died for sure at some point if I hadn’t been monitoring my gpu temps regularly and kept playing games without knowing my card had been overheating.
It was just a matter of time till that would happen.
The culprit is most probably the Gigabyte bios for the RTX 3000 series AT LEAST PARTLY, and while the issue seems to trigger as a combinational result of several factors (possibly due to software conflict with some other program, eg rgb software, etc), it is definitely related to the Gigabyte bios, as it is known to cause fan issues in some cases, here is a reddit post from 3 years ago for reference:
https://www.reddit.com/r/gigabytegaming/comments/jv7bcr/gigabyte_rtx_3080_gaming_oc_fan_issues/
Gigabyte sadly hasn’t released an updated bios version that resolves the fan issues with the RTX 3000 series cards.
The solution to the problem is either applying a custom fan curve with MSI Afterburner before running a game, thus bypassing the Gigabyte bios fan curve (recommended way), or flashing a compatible BIOS for the same card from another vendor (eg ASUS) on your Gigabyte card (unorthodox way).
If you have a Gigabyte RTX 3000 series card and you’re facing random gpu overheating, that’s the solution to your problem, at least for now.
And ALWAYS, I mean ALWAYS monitor your cpu + gpu temps with MSI Afterburner while playing games.
In short, in order to be able to play the game without issues and without worrying about possibly damaging your gpu, monitor your gpu vitals (temp, usage, frequency, fan speed) at all times with MSI Afterburner and set a custom fan curve before running the game.
Also, remove the Diablo IV Prefs file from the Diablo IV folder in the Documents location.
Normally you shouldn’t have to do all this just to be able to play a game, but as I always say, if there is something on our end that we can do to save me time, money and frustration, we should definitely do it.
Better be safe than sorry. 
I made a youtube video when this issue first occured and since then went through extensive testing to investigate the cause, you can check this post for more info:
https://us.forums.blizzard.com/en/d4/t/diablo-4-server-slam-cooked-my-gpu/21857/17