@AxelG Thank you, i finally got it to work but stumbled upon another problem during the installation in a virtual environment. The installer still uses setuptools from my main python install and the lowest version in portage is 62.6.0 which seems not to be compatible with the installer script that uninstalls it inside the virtual environment. After installing a lower version using pip (pip install setuptools==50.2.0) and installing pygobject as you mentioned in your post I was finally able to successfully install rpd.
Just in case someone wants to copy/paste the commands:
virtualenv --python=/usr/bin/python3.10 ~/RDP source ~/RDP/bin/activate ← change into the virtual environment python ./install.py ← this will remove the wrong setuptools pip install pygobject pip install setuptools==50.2.0 python ./install.py ← now it should sucessfully install rpd
today I ran into the exact same problem and it is still not solved, as now introspection is also needed. So atm I am not able to install RPD 0.9.34 on my laptop