Thank you all for the great input and sorry for the late reply.
I followed @Aleks advice with the plain vanilla debian. The installer indeed told me, that a driver is missing (in my case the “rtl_nic/rtl8168h-2.fw”).
So what I did to get yunohost running is
- Install yunohost via wizzard
- dismiss the post-installation
- mount an additional usb stick with the driver (source)
- sudo dpkg -i firmware-realtek_20200918-1_all.deb
- sudo dhclient -v enp2s0 (to obtain an IP from my local router, thanks @ljf
- perform yunohost post-installation
Because in my case after a reboot the computer did not obtain an IP, the dhclient -v enp2s0 command has to be performed at every boot. So i created an executable file with this command and added to crontab -e a line
@reboot /path/to/executablefile
Now it works seamlessly and I have to say it’s quite a leap in performance from a raspi to an i5 
Thank you again for the support and the awesome project!