The active and instrument flags are mostly used to disable instrumentation.
In this case, the agent still tries to establish a connection with the APM server and collect and send metrics. I believe this shouldn't affect your dev env, it only writes to the log.
If you add ELASTIC_APM_METRICS_INTERVAL: 0s (see config option documentation), metrics collection will be disabled.
In addition, you can add ELASTIC_APM_LOG_LEVEL: ERROR to remove agent loggings.
This doesn't mean no agent code will run at all, for that you need to remove the agent altogether. However, it may be enough for your purpose.
I hope this helps.
Eyal.