P: Search or Filter by Pixel Dimensions, Long Edge Dimension & Aspect Ratio

Merging with more appropriate topic.

Please reference the new conversation here: Lightroom: Filter by crop aspect ratio

Merging with more appropriate topic

Please reference the new conversation here: Lightroom: Filter by specific aspect ratios

Merging with more appropriate topic

Please reference the new conversation here: Lightroom: Bizarrely lacks sort by file size function

Merging with more appropriate topic.

Please reference the new conversation here: Lightroom: Why can't I sort by image size and dimensions

Merging with more appropriate topic.

Please reference the new conversation here: Lightroom: More sort fields

Merging with more appropriate topic.

Please reference the new conversation here: Lightroom: Ability to sort images by aspect ratio/pixel dimensions

"Sorting by File Size would allow us to quickly skim the thumbnails to find duplicates!"

In addition to List View, this article describes two plugins that attempt to find duplicates directly: https://www.lightroomqueen.com/clean-duplicate-photos/

"How can this be classified as "Implemented" when it is merged with a function that does not exist? 
I see we can sort by Aspect Ratio; however, that is NOT the same as File Size."

This topic hasn't been well-curated, obviously, and some of the confusion results from ambiguous terminology.

The original request, searching for images based on their pixel dimensions, was implemented years ago in smart collections, which is why the topic is marked "implemented".  

Some of the subsequent requests merged here are for searching or sorting by aspect ratio.  Smart collections and filters search by landscape/portrait, which most people and standards call "orientation" but LR confusingly calls aspect ratio.  LR doesn't provide any way to search for numeric aspect ratio (e.g. 1.5, or 3:2, whatever), but you can sort photos by numeric aspect ratio using View > Sort, which gets the job for most use cases.  If someone still wants the ability to search by numerica aspect ratio, I think it's best if they post a new feature request.

And then some of the requests merged here are for searching or sorting by file size.  While LR lets you search by total megapixels (one measure of size often used in digital imaging), you can't sort by megapixels. And you can't search or sort by file byte size (another common measure). It looks like the best topic to add your vote for searching by file byte size is here:
https://feedback.photoshop.com/photoshop_family/topics/a_better_search_find_in_the_library_module_li...

I'll try to re-merge some of these later requests into more appropriate topics.

You could try this plugin by John Beardsworth

http://photographers-toolbox.com/products/jbeardsworth/listview/index.php?sec=use

How can this be classified as "Implemented" when it is merged with a function that does not exist?

I see we can sort by Aspect Ratio; however, that is NOT the same as File Size.

Particularly when dealing with smartphones and backups, duplicates can have different timestamps, filenames, etc., but still be the same (or nearly so) image with the same file size. Sorting by File Size would allow us to quickly skim the thumbnails to find duplicates!