Also, a farfetched suggestion may be that they are using an older operating system.
I had a Windows 7 install that was so old it couldn’t update and had trouble with installing programs.
This error is likely caused by his internet configuration blocking the gdevelop-app.com domain name. They should check that their firewall/proxy/parental controls/adblocker/vpn/network administrator/etc whitelisted at least these domains:
Thank you so much for all your suggestions to help my student.
He has his lessons at school while I Zoom in remotely and it turned out that even though GDevelop was unblocked on the school server, the subdomains were still blocked.
So unblocking those sites (as recommended by arthuro555) solved the issue.