First of all, thanks for coming to this thread and even considering helping me out. I've been troubleshooting for 2 days and am about to rip my hair out over this.
 
TLDR
I bought a used 3080 Ti. While the RGB and fans work just fine, this GPU seems to not be detectable by my motherboard and/or Windows 11. Device does not show in device manager and the VGA LED is lit up on my motherboard.
 
I'm looking to understand the most minimal process I can carry out in order to determine if this GPU is DOA or if I'm just garbage at troubleshooting.
 

Components
PSU: Seasonic Prime TX-750
Mobo: Asus Tuf B550M-Plus
CPU: Ryzen 5800X
No other PCIE or high-power devices have been installed.
 
 
Previous Troubleshooting Steps
1) Updated motherboard BIOS to newest (2803).
2) Wiped drivers with DDU.
3) Booted with a second GPU installed, Windows showed no indication that 3080 Ti was detected (enabled hidden devices in device manager).
4) Reset BIOS / cleared CMOS (no output even directly after doing this).
5) Tried various combinations of setting PCIE speed to gen 3, enabling/disabling CSM, enabling/disabling fast boot.
6) Started system with no GPU, let settle, turned off, plugged GPU back in, turned on.
7) Attempted to install Nvidia drivers, failed because no compatible device was detected.
8) Attempted to run DisplayID firmware updater, also failed.
9) Checked the VBIOS version printed on the card against the GPU-Z online DB. Both indicate the newest VBIOS is flashed (94.02.71.80.C0).
10) Installed the 3080 Ti into a Core X egpu enclosure. The enclosure was detected in Windows and Mac OS, however the GPU was absent from all device lists. RGB and fans on GPU worked fine.


Misc Notes
1) I've ensured that the PCIE slot still works with a VEGA 56 GPU.
2) I am using two separate cables between the PSU to the GPU.
3) I ordered a Seasonic PX-1000 just in case the PSU wattage is a potential problem. I'm pretty confident that this should not matter for getting a BIOS screen, but please let me know if I'm wrong.
4) All behavior explained above occurs no matter which output port I use on the GPU. This also occurs if I have none of the output ports connected.
 
 
If anyone has any further troubleshooting steps, holes they can poke in my troubleshooting, or even just general comments about how dumb I am, I'm all ears. Thanks in advance!

Thanks for the initial response, hopefully there's more where that came from!

Fully installed - yes, I make sure to check the latch and fully tighten the thumbscrew every install
Closest slot to the CPU - yes
Fast boot off - yes, along with various tweaks to other settings (bullet 5 in troubleshooting section)
Solid power connections - yes, these are double checked every install as well

The fans spin on boot, and they continue spinning while power is maintained.

I've attempted to utilize various combinations of two of the PCIe connections on my PSU. I've also attempted a number of cold boots (wiped startup files every time). Unfortunately I've had no luck.

Used all ports: Yep, I've even gone as far as to perform a cold boot between using each port. I have no output during the boot process nor is anything displayed after booting to windows.

Setting PCIE GPU primary: I have not been able to find a BIOS option to force a specific type of GPU. I'm not sure if this is because I don't have an iGPU or because my motherboard simply doesn't have that option.

1000W PSU: Estimated arrival is in 3 days, maybe 4 if it gets delayed for any reason.

Another PC: I've tested it in an extremely similar X570 platform, however with the new PSU I'll be able to test the it in a much different Sandybridge-based build.
 
 
Thanks for sticking with this btw, good to know I was at least barking up the right trees before coming here.

I know higher wattage is obviously not going to be detrimental, but could you help me understand why a 1000w+ power supply would be required to even just boot with this card? I'm currently working off of the assumptions that:
1) The max power budget is 375w for this card (2x 8pin + PCIE). I understand that spikes around 500w is common with some 30 series.
2) I don't currently see my system exceeding 450w under a full furmark/prime95 load with a GPU that uses 180w (monitored via GPU-Z). This would put the worst-case spike with only a 3080ti at around 770w.
3) I have a 750w PSU that, while it doesn't meet the recommended 850w for this GPU, should be enough to sustain short power spikes of 770w if they were to occur.
4) I shouldn't even be close to max power draw/power spike territory during boot, which means I should expect to see a BIOS screen or at least the windows logon screen through the 3080 ti's HDMI port.

Please let me know where my assumptions are incorrect. I'd like to figure out how applicable these worst-case numbers are considering I didn't expect them to be relevant during boot/startup. Regardless, I'm definitely waiting to see what happens with the 1000w PSU before making any determinations about this card.

That sounds like a separate issue. The four LED power lights on my card have a momentary flash during boot but that's the only time they're lit.

A quick search shows there's a reddit post with a dropbox link in the comments that might be related to your issue. I can't link it unfortunately. If it is related, I'd recommend only getting the firmware files from the link in the comments and getting the EVGA MCU Tool straight from github.

The BIOS will recognize the video card if good, you should be able to see and go to the BIOS. After the installation on the 16 PCI slot is correct. Next, Windows will recognize too. However, if you CPU has video capabilities, then it will need to be disable, the CPU GPU can not be together with sole GPU.

Pm me the link to it  I've been trying to find a fix for this issue

Mystery solved. A second GPU of the exact same model works just fine in my current configuration. Since the "bad" card has a sticker with the newest vBIOS printed on it, I'm going to assume the initial 3080 ti is bad.

Hopefully this thread can help someone else figure out the difference between vBIOS issues and a dead card faster than I did. Thanks for the assistance, everyone.