Can I Disable Windows Defender When I Have Bitdefender??

As @Gjoksi said the windows defender should have automatically been disabled if bitdefender was installed.

If it did not, you can disable Windows Defender and shutdown all processes of this antivirus when you have Bitdefender. However, it is not recommended to do so, as Windows Defender can provide an additional layer of protection against malware.

If you do decide to disable Windows Defender, you can do so by following these steps:

1) Open Windows Security.

2) Click on Virus & threat protection.

3) Click on Manage settings.

4) Under Real-time protection, toggle the switch to Off.

Once you have disabled Windows Defender, you can shutdown all processes of this antivirus by following these steps:

1) Open Task Manager.

2) Click on the Processes tab.

3) Look for the Windows Defender process.

4) Right-click on the Windows Defender process and select End task.

Regards