Lightroom Classic: Complex / Advanced Search
Lightroom's Library text search function is very rudimentary, far from what is possible with SQL, the database engine underlying Lightroom's catalog.
The default text search is a logical AND ("contains all" or "contains words") which finds photos with all the entered search terms in whatever field is being searched (keywords, captions, or both). You can find terms that begin with a phrase (+begins) or ends with a phrase (ends+) and photos that do not include a term (!exclude). That's it, as far as I can determine.
There is no logical OR capability. For example, there's no way to search captions that contain Morus OR mulberry.
It would also be very handy to limit searches to folders with a particular name. For example, search in all folders that have Garden in the name, or all that have Portrait in the name. In my file system there's one of these folders for each year going back more than 20 years so searching each one independently is tedious and time-consuming in a catalog with over 348,000 images.
Lightroom, at its core, is a database with a develop module. However, the database aspect has been ignored from the beginning.