For anyone that landed in here after migrating the apiVersion to v1beta1, there are new attributes that need to be specified:

Similarly, in v1beta1 of the OpenTelemetryCollector CR, leaving out this configuration altogether also results in the Target Allocator failing to discover scrape targets from your ServiceMonitors and PodMonitors.

Reference: https://opentelemetry.io/docs/kubernetes/operator/troubleshooting/target-allocator/#did-you-leave-out-the-servicemonitorselector-andor-podmonitorselector-configuration-altogether