There is an addon tool that can be used to use various expressions in the 'Quick Filter Bar' (Ctrl + Shift + K) https://addons.thunderbird.net/en-US/thunderbird/addon/gmailui/

The Global Search is really filtering on specific keywords and then allowing extensive filtering where you can state must include or not include any filter in the left pane to refine the search, but it offers AND in keywords section. It does offer a specific combination of words. https://support.mozilla.org/en-US/kb/global-search

Thanks.

So, surprisingly, there is NO way by default to search for either of two or more items. Guess I'm spoiled by gmail's web interface's search options.

Thanks again, I'm trying out the add-on you mentioned.