Currently, the system only supports for Contact and Opportunity table that enable to view in the dropdown Related conversation button. Refer this document: https://learn.microsoft.com/en-us/dynamics365/sales/manage-text-message-communications#:~:text=Related%20conversation%20to,to%20that%20record.

It would be helpful and convenient for customers if we can add more tables in this button that help customer able to manage and control the custom to enhance their experience in this platform.