How can I gain some understanding about my lemmy instance?

Prometheus and Grafana.

Your lemmy instance should have an endpoint for prometheus metrics; https://domain.com/metrics.

Install prometheus (in a docker container) and setup lemmy as a target. From within docker, create a new network called prometheus and add your prometheus container and lemmy to it. Then using the data that prometheus pulls, you can setup a nice looking dashboard in Grafana like this: https://i.xno.dev/4nLNK.png

The dashboard above is for my private DNS DoH stub resolver. You’ll have to make the dashboard yourself because there are no public dashboards for lemmy.

This option is preferable because it all works with docker: https://i.xno.dev/cWjtR.png

And this is what the prometheus config should look like;

[xanza@dev prometheus]$ cat *.yml
#prometheus.yml
global:
  scrape_interval:     15s
  evaluation_interval: 15s
scrape_configs:
  - job_name: 'docker'
    file_sd_configs:
      - files:
        - targets.yml
#targets.yml
- targets: ['blocky:4000']
  labels:
    job: blocky
    __metrics_path__: /metrics

Have you considered engaging the Lemmy support community? I know they have a Matrix room.

This will show all the individual steps happening to configure an instance without docker: https://github.com/LemmyNet/lemmy-ansible