There’s a fancy ‘Find’ interface accessible not in both Jupyter Notebook (v7+) and in JupyterLab from the ‘Edit’ menu.
Once you have opened the ‘Find’ interface, you’ll see a filter icon near the middle-right, toggle that to adjust your settings. You’ll want to toggle on the ‘Search Cell Outputs’ option box to search for text in Cell Ouputs.
Guides to what you are looking for:
See Searching through Cell Outputs using CTRL+F in JupyterLab: Any Solutions? - #2 by afonit
(Here is what the ‘Find’ interface looks like in light form, from image in this post. See the funnel to the right of the cursor/hand in that picture. Toggle that.)