Stop connman from managing DNS
If you don't have any DNS configured in /etc/resolv.conf anymore, you can't resolv any domains on the internet. It's smart to install a replacement for connman's DNS in advance. Otherwise you can temporarily solve that by executing echo "9.9.9.9" | devel-su tee /etc/resolv.conf
You need to add the --nodnsproxy proxy flag to connmand. This can be done by runing devel-su systemctl edit connman and pasting this into there:
[Service]
RuntimeDirectory=connmanAfterwards run devel-su systemctl restart connman.