Headwind MDM can get the serial number and the IMEI, also in Android 10 and above (these Android versions have restrictions for getting IMEI and serial number).
However the serial number is not included in the API (
https://h-mdm.com/headwind-mdm-api/) because the API is public and any third party app can use it. Headwind MDM is made compliant with Android best practices which do not recommend that any app can retrieve the serial number.
Headwind MDM is open source so you can rebuild the source code and add the method for serial number retrieval.
If you're purchasing the Enterprise version, this customization will be done for you at no additional charge.