Search a text in an Execution Plan

I can use Ctrl+F and search inside the EXEplan for every test/folder that has that substring in its name. is that what you mean?

Quick answer. No.

However, you can search the contents of the .mds file. This is the project file, which includes the execution plan.

If your search is intended to be within a test itself (dynamic) and only concerns the name or description of the tests in the execution plan, you can still dynamically retrieve their values via script from the following object and its properties :

Project.TestItems.ItemCount
Project.TestItems.TestItem[Id].Name
Project.TestItems.TestItem[Id].Description