Dear Amol Vaidya
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
Based on your description, it seems that the VSTO excel plugin user interface can't show correctly in Excel 365 but can work well on other Excel versions.
Per our search, the VSTO excel add-in should created in Visual Studio, and this query is belongs to Visio studio, which is a built in feature. We also want to do a test for this to help you, but as engineers in here have limited experience in Visual studio,, which is out of our support boundary. We have no enough test resource and environment to help you do the test. For such a developed scenario, we really hope you can get dedicated assistance to further investigate. Kindly post a thread in Visual studio community to sign in and select ask a question . The engineers and community members there are specialized in this query connected with other server environments. I sincerely hope your question can be addressed by experienced assistance.
Thank you for your cooperation and understanding into the Microsoft Community. If you need any further assistance, please feel free to post back.
Sincerely,
Stacey | Microsoft Community Moderator
