I used to use MQTT, static_status and Healthchecks.io, and have that data passed through to Home Assistant, but it started to get pretty cumbersome as the amount of machines I had grew.

I now use just Zabbix and HealthchecksIO. I did need to spend some time writing new templates for some additional data I wanted to collect (like SMART data for SSDs that provide health metrics in non-standard attributes, and HealthchecksIO so I could see the status of various checks on my zabbix dashboard)

Zabbix also has some additional features I found appealing, like proxies that can continue recording data when the main server is down, and built in encryption. Some checks like open ports/icmp responses etc can be checked using either the local agent, the remote server, or both, which helps quickly diagnose things like firewall config issues.

I did look at some other solutions, but I wanted something integrated to hit the ground running. Mobile apps are very limited, and there is no official one to my knowledge. I use Moobix which I don't believe is FOSS - but I could be wrong there

Try each solution out and see what works best for you!