macOS (Catalina 10.15.7) - Save dialog - no way to filter/search In macOS, the Save dialog window has a search box, seemingly to allow for users to search/filter the output in order to use an existing file/folder name as a template to then modify for the new file/folder, however when you enter anything into that search box, the output window shows nothing. Contrast this to the Open dialog, where the same search box behaves as it should, and filters the output window accordingly.
The behavior with the Save dialog is recreatable in any app, including the Apple-provided native apps.
Just to clarify what exactly I do (on other OS'es without a problem), here's an example:
Let's say I have an existing file named &quot;File blah blah blah 12341242.txt&quot; and I want a new file named similar but with different numbers in it. On Windows and Linux, there are no issues with clicking an existing file in a Save dialog to have it fill in the file name of the new file with the name of the existing file so you can then either save it as that name or modify it as needed.
In macOS, however, the only way to do this is to manually scroll through the output window to find the existing file. But, let's say there are thousands of files there and you don't remember exactly what the existing file's name is. You go to the search box to search for a word or number of the file that you DO remember, only to find that the search box doesn't work (effectively), so you're out of luck.
Is there some way to remove this restriction or modify it to allow the search box to function as a way to filter the output in order to use the output as a template for new files/folders?
Edit 1:
Here are 2 screenshots to show what I mean.  These are from the Preview app, for the record, so you know it's a default app and not third-party.
Screenshot 1 - Showing an existing file name in the Test folder:

Screenshot 2 - Showing empty search results even though the existing filename matches the typed text:

Edit 2: Here is a short screen recording of the problem in action, if it helps better than still images
Screen Recording
I think the crux is searching for a folder vs searching for a file.
Search in open and save works as well as Finder for me - just a different interface and limited space, less affordances are present, but as a long time user of search, perhaps I just have gotten used to the limitations and don’t even see clearly how it’s failing you.
When I need more space to search, I open a second Finder window and use spotlight search (sidebar search, tag search, Smart Folders, complex searches) to my hearts content and then drag the file I find into the save box.
It really helps you can drag and drop folders and files and they instantly update the file open and file save dialogs.
Any time this doesn’t work, I find one of two things.

The app isn’t using a standard dialog. You need to patch that app or select a new app so things are easy again
Spotlight itself is failing - this is easier to detect in Finder for me, but you can also detect this in app file dialogs if you are keen and know the results should show and do not.

The key win for me is having second display and drag/drop of files from outside the save box. You also might love a tool like DefaultFolderX - I used it heavily years ago but have gotten used to working with the OS and not needing extensions.

https://www.stclairsoft.com/DefaultFolderX/

The author is a long time supporter of Apple users and has superb value / customer support in my experience. The tool does amazing things - I just work on so many macs, that in stalling a bunch of tools doesn’t work for me unless I can’t live without that tool. Don’t take my not using it to mean it’s not awesome - it is absolutely amazing and well worth a trial.