How does an upgrade of FortiClients is performed via FortiSASE?
As of right now FortiClient upgrades are performed via customers' MDM solutions.
At the time of this writing the FortiSASE operations team will upgrade existing FortiClients 7.0.3 to 7.0.7 - https://status.fortisase.com/incidents/01mdzy0crg7h (exceptions apply - contact FortiCare Support (https://www.fortinet.com/support/contact) and reference FortiSASE Operations ticket #47560 ). New FortiSASE deployments won't be forced with an upgrade to 7.0.7.
It is planned to add an ability to schedule FortiClient upgrades via FortiSASE GUI console in the later releases of FortiSASE.