The only option you can find related to Bitlocker is "Require" or "Not configured".
You need to create a custom OMA-URI policy to enable the setting "Security/PreventAutomaticDeviceEncryptionForAzureADJoinedDevices" in Policy CSP.
Here are some posts with the similar issue with yours, just for your reference, you can try the method mentioned by Mark_Thomas:
Hope above information can help you.
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