No “Search Folders” entry under “Edit” Menu
To create a search folder, https://help.gnome.org/users/evolution/stable/mail-search-folders-add.html.en says: “Click Edit ▸ Search Folders, or click Message ▸ Create Rule and select the criterion the search folder will be based on, or if you have run a search, click Search ▸ Create Search Folder From Search….”.
Under the “Edit” menu I have the options Cut, Copy, Paste, Select All, Delete Message, Undelete Message, Find in Message…, Accounts, Message Filters, Plugins, and Preferences.
As the menu does not allow me to select a virtual folder for searches, I cannot search all folders for a string.
Note that I have downloaded all messages from the server locally.