iMac mid 2011

Hello everyone, I have a problem that makes me unable to install monterey on my mid 2011 imac. It is connected via Ethernet and I use an external ssd as the installer. I made a partition to install Monterey because I was scared of losing high sierra and I was right to do so because I eventually end up on this screen making me unable to finish the installation process. If you guys have any suggestions I would love to read them