Right click on the windows task bar choose Task Manager, Performance and check out the graphs to make sure nothing is maxing out.
Turn off any VPN products; Encryption, extra hops and Shared bandwidth at the far end all account for VPN and Video being at odds.
Check your Antivirus! Many AV products include a local proxy and when your PC is under heavy load, your latency suffers. Some products allow you to right click the tray icon and choose “Disable for an hour”
Use a Skype call between 2 local phones to diagnose Wifi, as Skype is a peer-to-peer technology.
Wifi is a shared medium, meaning your neighbours can effect your Wifi quality; If Video or Audio call quality is choppy, find an Ethernet jack to plug into. May not be a long term solution but you can get a comparison to narrow down the problem. Your cell phone status bar gives a rough idea of quality shown by number of white waves in your Wifi indicator.
If you have multiple Wireless Access points you can ensure you are connected to the closest one by disabling your wifi, waiting a 5 seconds and re-enabling it.
If both laptop/phone and Wireless Access Point support 5Ghz it usually not as congested as 2.4Ghz.
Most router allow you to logon via a browser and check for high CPU and memory usage. In a command box type “ipconfig /all” to show your default gateway. In a home setup that IP will be your router.
If your Router is over 2 years old, its time for an upgrade. If more than 3 people use the internet at the same time or for streaming video or gaming, consider a gaming router. You can also use OPNsense or PFsense to turn an old laptop into a firewall for free.
Search DownDetector for your ISP and you can show outage by geography.
Run a speedtest and pay attention to your upload bandwidth. A consumer grade internet connection will have an upload bandwidth only 10% of its download bandwidth. But Video conferencing requires good bandwidth in both directions. You might want to test this at the end of your conference call.
DownDetector can quickly tell if a service, such as Microsoft Teams or Zoom is having problems. There is a search bar at the top and a nice graph to show history.