By default, call forwarding on your Huawei device is set up by mobile carrier standards. Usually, calls will be forwarded if your line is "busy", there is "no answer" or your device is "not available". The forwarding can be (de-) activated for each case by itself, or you can set up a different phone number as a call receiver.

Android 10 | EMUI 10.0
Step 1:  Open the  Phone app
Step 2:  Open the  menu
Step 3:  Open the  settings
Step 4:  Tap on  Call forwarding
Step 5:  Choose  When busy ,  When unanswered  or  When unreachable
Step 6:  Confirm with  Change
  1. Open the Phone app
  2. Open the menu
  3. Open the settings
  4. Tap on Call forwarding
  5. Choose When busy, When unanswered or When unreachable
  6. Confirm with Change

Huawei Instructions