AssetAccountant will detect assets entered into Xero only AFTER you have setup the integration and they are added to an account with the account type of 'Fixed Asset'.
You can quickly check your chart of accounts to see which, if any, accounts are set up in this way in Xero:
To test this is working, try coding a fixed asset acquisition transaction to an account of this type in Xero, then have a look in AssetAccountant - you should then have the option to Add or Ignore any such transactions.
For existing assets in Xero, you will need to import them into AssetAccountant
You can easily export these from Xero and import them into AssetAccountant.
You should import your existing assets into AssetAccountant with an opening balance -> which is the date that becomes the line in the sand from when AA will now handle all of your assets and journal postings.
Please see this Xero article for details of how to export your existing assets in Xero:
Once you subscribe to AssetAccountant and integrate it with Xero, AssetAccountant becomes the source of truth for your fixed assets.
No longer Xero.
So after you enter these assets in Xero and map the asset groups, you will no longer see the depreciation here.
Refer solely to AssetAccountant and all of the reporting that is supported in your account.