Before I start, I want to help you all with your time and advice given.

Whatever I do, the GND pins of my STM32H753ZI are impossible to solder. The rest of the pins are quite straightforward and easily soldered at 350°C after 3 seconds of heating. The ground pins, though never. I tried increasing the temperature to 400°C and increasing the amount of time heating, but still nothing, the soldering just doesn't go there, even with a tone of flux.

I use the Yihua YH-936 soldering station, so I have a very fine tip. Idk if that's the issue, but as a beginner, I don't really know.

I need some guidance because I have already destroyed one of these pins (I accidentally pulled it out while trying to fix my solder there), and by continuing that route, I'll have none left.