Thank you for contacting Syncfusion support
We have checked your reported issue, we are not able to reproduce it in our end. We have prepared a sample MatDialog with Dropdrown button. Please find the below sample link.
Please provide the below details:
1. Please replicate your reported issue in the attached sample.
2. If possible, please share us the issue replicable sample.
Could you please provide the above requested information, based on that we will check and provide you a better solution quickly.