I didn’t know SC had structured queries either! I would’ve used ref: in particular
I see where this link is found now at the bottom of the search bar:
and that structured queries are mentioned near the top with the
in:ebs example, but I definitely think it could be made more visible
I can write up an issue for some improvements to the existing search. In particular, I think having a “Filters 
” dropdown button in the search bar (left or right) or just below it would already improve it a lot.
Lots of websites already have this, so it is somewhat of a UX convention. Some examples being Amazon and GitHub:
GitHub in particular updated the search UX a few years ago. Prior to that it was very similar to the current SC experience where there was a page describing filters and you could type them in, but there weren’t many other indications.
When you click on a filter in the dropdown, it could just move the filterX: text into the search bar.
As a first pass, could even just have the “Filters 
” button just link to the /search-filter page, with no other interaction initially, just a more explicit button
Additionally (can be added later), if a filter is fully written out, the UI can convert it to a pill shape inside the search bar to differentiate it from the plaintext query. Or do it similar to GitHub with the highlighting, or current SC with the text color change.
Tangentially related, but I see it also says “Search by algolia”, but I thought SC’s search was custom built on ArangoDB? (Hence this thread etc). I haven’t read through much search code yet, so I might very well be just missing some nuances 