Check out this documentation for more detail information to date.Device Utilization - Cisco Meraki Documentation

As of MX 19.1, Cisco Meraki will no longer support USB-based Cellular Failover on the MX and Z platforms.Legacy products noticeWhen configured for this version, Z1 devices will run MX 14.56.When configured for this version, MX400 and MX600 devices ...

Have you tried to block UDP 443 so that the QUIC protocol now has to be forced to use the SSL inspection process?Managing the QUIC Protocol | Zscaler