Usually the error message “Our systems have detected unusual traffic from your computer network” appears when using VPN connection, proxy tunnel, system like tor browser and other situation like DNS over HTTPS (DoH).
Unusual traffic on Google because the Google system thinks you are a robot or a virus because you are making too many requests in a short period of time.
If you are using a system like I cited above, the error message is normal because you are using a shared IP address and Google interprets your request and any other requests made by other users using the same IP address as if they came from the same place. In short, you have the option of telling google that you are not a robot by completing their recaptcha to confirm that you are indeed a human.
Other situations can also cause the problem “unusual traffic from your computer network detected”, for example, you have a malicious program on your computer, a bad extension in your browser or a problem with the configuration in your router.
How to fix unusual traffic on google
Disconnect your VPN and proxy connection.
Disable all suspicious addons on your browser.
Open your browser in safe mode, then if the problem stops, reset your browser.
Uninstall any suspicious programs you have on your system.
Scan your computer with anti-malware and anti-virus.
If the problem persists, restart your router.