A few years ago, I was playing on my 3DS, while suddenly the game didn't work anymore. I turn it off and back on again, but I couldn't do anything on the home menu anymore. The only thing I could still do was pressing the A-button to start the game. While playing the game, the touch screen barely responded and was completely decalibrated. When I tried it again a few days later, the touchsreen didn't respond at all.
The only things I can still do, is playing games (without the touchscreen). Also, when I blow or tap on the touchscreen, the icons on the upper screen still turn around. So the touchscreen still 'knows' I'm touching it.

Because my 3DS was already 3 years old back then, I just bought a new one (a 2DS). But I'm still wondering what could have happened to it. I couldn't find any information about this problem on the internet, but maybe one of you guys knows what it could be?

AFAIK the icons on the upper screen on the main menu is turned around because it detect sound using the microphone, not the touch screen. So my best guess is the broken touch screen.

Spinning icon is indeed the mic and not the touch screen.

This happened 3 years ago and you're checking it out now? you didn't care to check for 3 years why does it matter now? But yeah, this touch screen is most likely dead

Could try going into System settings > Other settings > touch screen
see if you have any luck with the calibration software but yeah... this happened 3 years ago, hard to want to expend energy going in depth with this assistance if I'm honest.

Looks like the touchscreen is broken, since the spinning icons is with the microphone

But does anyone know what's up with the home menu? I can't use the circle pad or d-pad to go to another software.

Open up your 3ds poke around and snap it back together again. Google a video tutorial first though.

All I can think of why the dpad and buttons not working right. The touch screen could be stuck "on" pressing. While you're trying to use the Dpad. Both inputs are being canceled out.