NextJS has OpenTelemetry embedded in the framework however, to use it has a few more steps to configure. For Google Cloud Trace, that step including updating next.config.json to exclude library that suppose to run in the server side.
The official guide from Vercel is here which using OLTP to export the data. However, Google has their own package for exporting trace data @google-cloud/opentelemetry-cloud-trace-exporter
Document in Google shows how to configure the OpenTelemetry which can be use with Vercel document and add to instrumentation.node.ts file. After follow the google document, add google-proto-files into the serverComponentsExternalPackages in next.config.js file and the trace data should appear in the cloud trace dashboard.