The MS350 switch is a Layer 3 switch, but it does not support the same level of routing functionality as a dedicated router or Layer 3 switch like the Catalyst series.
In your case, you want to set up a backup static route with a higher metric for when the primary connection goes down. Unfortunately, this feature is not available on the MS350. The static route on an MS350 is a global setting and affects all devices.
As a workaround, you could consider using a more advanced router or firewall that supports policy-based routing or failover functionality. This device would be placed between your MS350 switch and the internet connections, and would handle the decision-making process for which path to use based on the availability of the internet connections.
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
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