Old write-up, but it worked AOK for me just now on Pi4B.
Node exporter is a great way to monitor your Raspberry Pi with Prometheus. Follow these steps to get node exporter running on your Raspberry Pi.
Before I forget how to add devices to Prometheus…
user@docker:~$ sudo nano /etc/prometheus/prometheus.yml
That is fairly simple file to figure out. Once saved, log into Portainer on the Docker LXC and restart the Prometheus container. To make sure it is working, log into the Prometheus web page and make sure everything shows as up. Then jump over to Grafana and the device should pop into the list.