Does it run a desktop ?
Or can you x11 export DISPLAY to a Linux box with desktop so you can run below to check profiles:
sudo nm-connection-editor
I dont know where network-manager stores its profiles so cant help you with that.
Do you need network-manager as Pi-hole comes with its own network manager called dhcpcd5 ?
If not, below one disables it at boot:
sudo systemctl disable network-manager
Check with:
sudo service network-manager status