Is there a way to easily browse photos or search / filter by media type in iCloud Drive or must one manually dig through each folder and manually open and close each photo one at a time?
No. (somewhat dependent on your definition of "easily")
iCloud Drive is NOT an app to manage photos, hence the reason it is not considered by some as "good at it". It's not the correct tool for the task.
Like using a hammer to drive screws. It sorta works but is not a pleasant experience.
The Photos app itself is where one can effectively manage their photos.
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