Thanks for all the suggestions. The approach with smart collection for file types and file names alone didn't work for me. Perhaps I did it wrong.
But I re-visited my process and used a bit different approach. Now I'm quite satisfied as it's consistent and does not require additional work from me except adding 1 keyword.
1) I select photos I want to either Enhance or Export to DXO
2)
Before running the process, I add keyword to them that I will be always using from now on:
_HasDenoisedVersion_
3) I do the processing and I end up with denoised copies always having
Ehanced or
DXO suffix in the name.
4)+ I have created filter preset in Library Grid: Files that has keyword
_HasDenoisedVersion_ + filename
doesn't contain "enhanced dxo" - This filter will show only
RAWs (noisy) that were processed/denoised. Filtering by filename was needed in my case as these processed copies contain the same metadata as originals, so will contain the same keyword as in point 2.
And now anytime I get back to this folder and plan to export only the "good" versions from mix of other RAWs and denoised photos,
- I can use this filter preset to select these original noisy RAWs that were processed
- then disable filter none - selection still stays
- Click Edit->Invert selection - this would select only the correct files for export - either RAWs that didn't require processing + denoised photos without noisy originals.
Unfortunately Library filter does not allow OR/AND conditions for the Text field nor does allow "inverting" current filter, so that's why this inverting selection is needed.
Alternatively I can create smart collection for files that: ( have DXO or Enhanced in the name ) or (are RAWs but do not have _HasDenoisedVersion_ )
Collections are more flexible as you can combine multiple conditions - depending on the need.
But of course there are many other ways of doing that based on flagging or labels. That depends on individual workflow/preference.
Thanks for your input