There doesn’t currently seem to be a direct way to go about those search methods, as far as I’m aware.
The closest equivalent I know of to search by title:
Go to the search page of the instance of your choosing (ex. lemmy.world/search, or lemm.ee/search). Larger instances will tend to be more useful for this since they are more likely to be aware of posts from any arbitrary instance; if you know that you want to search within a particular community, then searching on that community’s instance would yield all possible results, which could potentially not happen with a non-local instance search.
Filter to search only posts. This will yield both posts with the term in the title as well as posts with the search term in their body text.
Use your in-browser Find tool (ctrl+F for Windows, or Command+F for iOS desktop, or other methods with other OSs/devices) to search for the same search term on each page of results to highlight only the posts which have the term in their title.