Using SetAttr DESCRIPTION you can set the description on a file. You can then add a column to the lister to display the description.
Unfortunately, the quick filter seems to be unaware of this data. When you enter text into the quick filter which matches some description it doesn't pick it up.
Should it?
The quick filter only matches filenames.
Tools > Find Files > Advanced can search for files by descriptions, but is obviously not as convenient if you want to do it quickly and often.
Find As You Type can sort-of help here as well, if Preferences / File Display Modes / Details / Sort-field specific key scrolling is on (you probably want Preferences / File Displays / FAYT and Filter Bar Options / Search anywhere in the filename on as well). If you then sort by the Description (or User Comment) column, you can type part of a description and Opus will select the first file with one that matches. F3 can then cycle to the next file, etc. Not great if you want a list of just those files (Find Files is better for that), but may help if you just want to quickly locate one, or each one in turn.