This is most likely a DNS or VPN or antivirus issue.
In the end it's an internet issue on his side.
If you want help you nees to give info on all this topic: any VPN installed, any DNS changed, what antivirus etc
Also do the methods listed here one by one and carefully. I doubt that using a VPN for example would not work.
https://plutonium.pw/docs/update/#fixing-failed-to-check-for-updates
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