Hi guys, I am going to buy a Raspberry 4, so I need also a soundcard.
What do you recommend me?

thanks

If you have the money: https://blokas.io/pisound/

Neat product works well with pd!

If the pisound is in your price range it may also be worth looking into the Bela products, the Bela-mini would be about the same price as a rpi4+pisound. I have no experience with either, just toyed with the idea some and have researched the options a fair amount. The cheaper rpi soundcards all seem about the same with there being two varieties, the $10 to $20 bare bones type and the ~$50 hifi ones, I can find no good comparisons between them and many seem to use the same ADC to I2C chips, (or was it SPI?) I am skeptical that there is much difference in quality between the two price ranges here but some have a full or near full ground plane on the underside to shield them from the rpi, which would likely decrease noise, but that depends on more than just there being a ground plane though and they could be noisey despite having it. pisound seem to be the best option if you need good audio input as well as output, input options are not the best for the rpi.

I would also suggest PiSound, combined with the operating system they make specific to use with Pisound and comes with PD preinstalled.

PiSound:
https://blokas.io/pisound/

Patchbox:
https://blokas.io/patchbox-os/

It's very easy to setup. It even comes with simple ways of using it as a stand alone device. You can then use an Ipad or an Android device to change pd patches.

You will have it up and running in a day

Had to give up the first time I tried make a Pi3/pd based synth. But with Patchbox and and PiSound, it took only a few hours

I have a PiSound

It also does MIDI (with Din in and out plugs) which I have not used.

It works well. Stereo in and stereo out via 1/4" stereo plugs.