You can plug your custom data into the Analytics app.
Monitoring makes sense in an external tool, since it is complex and if Nextcloud is having a problem… you’ll want a separate service to remain online and tell you what is wrong in gory detail.
Matomo / Piwiki app is a popular analytics choice for monitoring your Nextcloud remotely using Matomo.
Prometheus is a top notch monitoring app, which displays beautiful grafana data.
Glances is an insanely good commandline tool. Can you be run client/server between your remote Nextcloud and your local pc. Supports containers, bandwidth, and everything else you can throw at it. Looks just like basic top/htop, but vastly more full featured. Restful api, optional webui, exports to any system you can imagine. This is my recommendation. Just figure out how to send it’s info back to the analytics app and/or track it directly from the glances app.