This might help you to get started https://giuliomagnifico.blog/post/2022-06-02-my-network-home-setup/
Not tried it myself but as far as I know you need
- Openwrt package prometheus-node-exporter-ucode for basic metrics or
- OpenWrt package collectd-mod(many options) + package collectd-mod-network + collectd exporter on the server for advanced metrics
Also nice to have are traffic metrics https://github.com/mstojek/nlbw2collectd
Next to the above you need Prometheus on your server to store metrics