In windows it's very easy. How come in linux there is no solution?

I have already tried using hda-jack-retask, but it was updated in 2014 last time and now its 2020 with Ubuntu 20.04 LTS. A lot has changed.

So i tried it out (hda-jack-retask), which seemed to work but messed up with my Xfce4 desktop, and audacity was buggy/crashing/doing weird stuff.

Never any of this happened before i use starting hdajackretask.

Also i cant change the settings in PulseAudio control, becuase if i plug in my headset, the built in mic is automatically unplugged. There is no option to do this.

Can someone help me?

Are you using a headset with included microphone, with 4 conductors on the plug? That may be problematic. A regular headset should work, though. The headset with mic should also work, but I've never tried it. You need to go into the pulseaudio settings, on the configure tab, and disable the headset mic, and make the built-in laptop mic the default. I've never used hda-jack-retask, never even heard of it, so I can't comment on that, other than to recommend removing it and using pulseaudio. Is pavucontrol installed?

hda-jack-retask used to work, but it's difficult to understand because it works on a very low level. Maybe it doesn't need an update.
But I don't see how it could "mess up" your desktop.

Here are some articles to get you started:
https://duckduckgo.com/?q=ubuntu+disable+headset+mic
I did not take a closer look.
Of course you are free to formulate your own web searches.