I'm curious to see what others use, but I've been using Uptime Kuma for this purpose at several different sites I manage. I run Uptime Kuma on a VPS and locally on site. I have the local instance monitoring the router, gateway, DNS, and several other internal and external devices. I also have the local instance do a "push" check-in on my VPS instance. This gives me a pretty holistic view of things.

Maybe smokeping?

https://github.com/linuxserver/docker-smokeping

Depends on how much you want to set up. For my purposes, I just check for connectivity every minute, and record true or false as a new row in a sqlite database if there is connectivity.

This is what I use on my raspberry pi,

#!/usr/bin/env python3
from datetime import datetime
import sqlite3
import socket
from pathlib import Path

try:
    host = socket.gethostbyname("one.one.one.one")
    s = socket.create_connection((host, 80), 2)
    s.close()
    connected = True
except:
    connected = False
timestamp = datetime.now().isoformat()

db_file = Path(__file__).resolve().parent / 'Database.sqlite3'
conn = sqlite3.connect(db_file)
curs = conn.cursor()
curs.execute('''CREATE TABLE IF NOT EXISTS checks (id INTEGER PRIMARY KEY AUTOINCREMENT, timestamp TEXT, connected INTEGER)>
curs.execute('''INSERT INTO checks (timestamp, connected) VALUES (?, ?);''', (timestamp, 1 if connected else 0))
conn.commit()
conn.close()

and I just have a crontab entry * * * * * ~/connectivity_check/check.py >/dev/null 2>&1 to run it every minute.

Then I just check for recent disconnects via:

$ sqlite3 ./connectivity_check/Database.sqlite3 'select count(*) from checks where connected = 0 order by timestamp desc;'

Obviously, it's not as full-featured as something with configurable options or a web UI etc, but for my purposes, it does exactly what I need with absolutely zero overhead.

You might be looking for a "smoke test"?

How micro are the cuts? You might get pretty far with the "ping" tool without any fancy monitoring setup around it.

For a while now I've had Grafana hooked up to InfluxDB and Telegraf. Using Telegraf I setup pings to ips along my route to the larger internet, major dns providers, and several large internet sites. I measure response time and packet loss. It has allowed me to cut through the Comcast BS when diagnosing problems with them. I can tell them for sure that the problem is inside their network and is the X hop from my router.

I recently started setting up Grafana over on a different server and I'm using Prometheus instead to monitor more than just the other server I was monitoring. I haven't yet set it up with that but it looks like something similar is possible with Prometheus based on the small amount of research I've done on it.

I use Uptime Kuma as mentioned in another comment, but also Speedtest Tracker which makes automated speed tests at the interval of your choice and displays them in a coherent dashboard. It’s pretty neat and it did help me figure out a few things about my network.