Is it grammatically correct to say that you wish to “study X at depth” (where X is some subject/field).
I thought you could say “study X at depth” similar to how you could say “study X in depth”, but I’m not so sure anymore
I think you might have (con)fused “in depth” and “at length” with one another.
The Cambridge Dictionary define in-depth as:
done carefully and in great detail
You might have studied American modernism in-depth.
The idiom at length is defined by The Free Dictionary as:
in great detail
I studied American modernism in college, so I can speak about it at length.