The POS UI Extensions Cart API has been updated, removing the email, firstName, lastName, and note Customer fields from the subscribable hook. Any extension used in POS version 10.0.0 or higher, and any extension targeting API version 2025-01 or higher, won't have access to these fields.
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/pos-ui-extensions-cart-api-customer-fields-removed-from-subscribable-hook