It’s unsupported and not guaranteed to work in the next version of Mylio, but this seems to work for me as either a search or a filter - that is, it finds images that have 1600 pixels one way or the other:
media:"mediaField(files, 2, 'height') = 1600" OR media:"mediaField(files, 2, 'width') = 1600"
The ‘2’ here indicates you want to search JPEGs - it would be ‘1’ for raws, but WhatsApp images are JPEGs. You could make the query more specific if too many non-WhatsApp images are included.
Here’s a strict version:
(media:"mediaField(files, 2, 'height') = 1200" AND media:"mediaField(files, 2, 'width') = 1600") OR (media:"mediaField(files, 2, 'height') = 1600" AND media:"mediaField(files, 2, 'width') = 1200")
This is gleaned from past threads on this forum from @Mylio_Deon and others. It isn’t supported or documented because we are making use of internal features of the app - and I see Mylio’s openness to this kind of thing as a major reason to use Mylio, in contrast with the closed-ness of other apps where you would never expect to get a developer response to such questions in the first place.
[Edit: just noting that the quote marks here are important - they should be ‘straight’ and not ‘smart’ -the quote marks in this sentence will be ‘smart’, but the highlighted text above should have