To delete a tenant first, you have to stop sending metrics to it, then 2 hours later, Ingesters will have shipped all tsdb blocks to the s3 bucket. Now you can delete the folder call tenant123 in the bucket.

The trick you mention with the compactor will indeed delete all blocks for the tenant as soon as the compactor finds them. This might be an alternative if tenants are still sending metrics. A better strategy is to block any requests on the proxy layer that has the org_id. Probably more effective in terms of storage.

If you want to this in the API, you need to enable purger component. The purger component will delete the tenant for you. Every time you call it
https://cortexmetrics.io/docs/proposals/tenant-deletion/