SigNoz uses Clickhouse DB to store metrics/traces/logs.
SigNoz otel collector exports to Clickhouse DB and SigNoz frontend/query service uses that data. So SigNoz otel collector is needed.
You can use export from your already working open telelemtry collector to signoz otel collector and keep using SigNoz.
SigNoz is an open-source APM. It helps developers monitor their applications & troubleshoot problems, an open-source alternative to DataDog, NewRelic, etc.