In infrastructures utilizing Fortigate firewall, it has been observed that users using the Chrome browser experience difficulties accessing certain web pages. No blocked applications, websites, or SSL anomalies are observed in Fortigate logs. The same users can access the mentioned web pages when using a different browser like Firefox.
In some threads opened on the Fortinet Community regarding this issue, it is stated that the Kyber Support offered by Chrome for the TLS 1.3 version is causing this problem.
Solution:
Disabling the function by entering the following code into the address bar of the Chrome browser has been seen to resolve the issue.
chrome://flags/#enable-tls13-kyber
Note: This solution is not permanent and may not work with future Chrome updates. It is recommended to await a permanent solution provided by Fortigate.
Source: reddit.com, community.fortinet.com