Dear Experts,
We have a custom button 'Demo' in a lead entity ribbon.

On Click of this button, we are opening a HTML webresource.

We are opening this webresource with the help of the alert.js library. We need to add the existing account and contact record in the fields available in this HTML webresource. Hence we have created a custom textbox attached with a lookup image (this field looks like a lookup field as shown in the above screenshot).
On click of the lookup image field, we have to show the account lookup dialog to a user from where the user can select the account record.
We were using Xrm.Internal.openDialog to open the lookupsingle.aspx dialog of account/contact and it was working as expected. However, recently we have updated our environment to UCI and XRM.Internal.openDialog is not supported in UCI.
We tried to open the lookup view with Xrm.Utility.lookupObjects, but it open the lookup dialog in disable mode and as a side panel of CRM window.
See the below screenshot.

We cannot choose the account record until we close the 'Target Lead' popup.
Please suggest any way to open the lookup view in the center of the screen so that it opens in front of the 'Target Lead' popup and user will be able to select the record.
Thanks in advance.
Regards,
Jay