Problem with Finder searches not finding anything

This is a problem I've had for a while, pre-update to Monterey. I think it's to do with the way my drive has built itself, and I'll explain. Please bear with me, because I don't know why it's done what it's done.

My iMac (Retina 5K, 27-inch, 2019) is showing, under storage, this:

Now, if I go to Finder and ask it to bring up some files based on part of the filename, for example 'Cornwall' (my photo filenames are descriptive. jpg) nothing is found. In fact, if I search for almost anything on my drive, nothing is found. Only files that are in the cloud, for example. So Finder is not indexing the files on my drive. It used to work fine, and I used only to show one disc. I'm not sure when the - Data part came along, but it would have been in an update perhaps?

I've lived without Search for a long time, but I'm beginning to get impatient. Has anyone got any good ideas, preferably ideas that do not involve deleting everything and reloading from start. I can do that, because nearly everything is already mirrored on a network server. But I'd prefer not to. You always lose something lol.