Since a while, the most recent macOS versions the system do report the use of «legacy system extensions» which is often triggered by modules or plugins of low-level software like VPN Clients, AV software etc.
The issue seems to be recognised by both vendors, as their support have stated that future releases of the software will address this issue by providing updates to the affected modules.
Please read the official statements here:
This is going to be resolved in newer versions of FortiClient, v6.4.1 and v6.4.2.
Bug ID is: 610586, so you can always go through Release Notes on new release of FortiClient and see «Resolved issues».
PaloAlto Cortex XDR
We are aware of the issue and we have been working with Apple towards the same goal since before Catalina was released. Apple will make changes in 10.16.
You can safely press OK (where possible) and ignore this message, it doesn’t have impact to the Agent. The next feature release will be compatible with MacOS 10.16, all you need to do is to keep XDR Agent up-to-date.