I recently discovered Beszel (https://github.com/henrygd/beszel) for monitoring all my homelab servers. It's quick, easy, and has a very clean and intuitive interface. Works especially well running inside of containers on hosts. I also wrote a very quick guide on getting it running inside of Kubernetes at https://github.com/henrygd/beszel/discussions/431.
While it's not nearly as powerful as say DataDog, it provides the core essentials of CPU, memory, disk, network, temperature and even GPU monitoring (via agent only).