In general, you won't hear back regarding most bugs you report (although some might be fixed).
Apple will get back regarding some bugs occasionally - whether to get more info or to inform you that no action will be taken regarding your report for one reason or another. It will usually take way more than 3 weeks (although exceptions do occur).
If you report on something more specialized than "macOS" - for example, Developer Tools - chances that you'll hear back are higher.