The most robust and mature way is to enable OpenTelemetry instrumentation and manually sending events within key methods or wiring up using suitable middleware if you use tRPC, next-safe-action or similar libraries.

The resulting traces and logs need to be collected and sent to a suitable service. In the beginning it'd make sense to use a third party service such as Better Stack. For serious long term it's reasonable to evaluate migrating to a self-hosted solution such as Grafana with its tooling.