Is 88°C under load too hot for my 3080 Ti?

If that reading is the GPU core temperature under a heavy gaming load, it is hot, but it does not by itself mean the card is about to fail. The card can reduce its speed if it reaches its thermal limit. Check the hotspot and memory temperatures too, since the core reading alone does not show the whole picture.

For now, reducing the power limit a little and capping frame rates can cut heat without needing a loud fan curve. Avoid leaving the computer running through the hottest part of the day if the room gets very warm. If temperatures keep climbing or the card begins throttling badly, stop and investigate rather than assuming it is fine.

The blocked fan and limited case airflow jump out more than the age of the case. If you can move that SSD adapter without causing another problem, restoring airflow around the GPU could help. A spare case fan aimed at the card, securely mounted and connected correctly, may also be worth testing before spending money.

Opening the panel is a useful diagnostic, but with a cat around it is not a great permanent setup. Keep the PC away from direct sun, and don’t put it somewhere cramped. If the side panel off makes a big difference, that points toward case airflow rather than proving the GPU itself is faulty.

I’d use the quieter, lower-power settings for the summer and accept a bit less performance. A frame-rate cap is easy to try, and a modest power-limit reduction often lowers heat and fan noise together. You have already tried undervolting, so I would not keep pushing that just to chase a particular temperature.

Also check the card’s own fan behavior and make sure every fan spins freely. If one is obstructed, fix that obstruction if you safely can. Adding fans or replacing the case can wait until it is affordable.

If the card is several years old and airflow changes do not help enough, worn thermal paste or pads are one possible explanation, but I would not jump straight to taking the card apart. Replacing pads can be fiddly, and the wrong thickness can make cooling worse. First check the temperatures with a monitoring tool and confirm the fans and heatsink are not obstructed.

If you are not comfortable servicing the GPU, keeping the power lower and gaming during cooler hours is a safer stopgap than an uncertain repaste.