Why do VSS Snapshots cause Availability Groups to fail over?
The failover policies are configurable - so you can adjust the thresholds
https://docs.microsoft.com/en-us/sql/database-engine/availability-groups/windows/configure-flexible-automatic-failover-policy?view=sql-server-ver15
of course to do this you need to know which policy triggers the failover in the first place
https://techcommunity.microsoft.com/t5/sql-server-support/diagnose-unexpected-failover-or-availability-group-in-resolving/ba-p/318474