Oddly, the endpoint on lemm.el and lemmy.ml return comments:

> curl 'https://lemm.ee/api/v3/comment/list?post_id=45734814' | jq '.comments.[] | .comment.content[:50]'
"Yeah, you're right. I didn't read enough of the do"
"Thank you for the tip ... but whatever I try with "
"~~In 0.19.5, they removed the deprecated `post_id`"

> curl 'https://lemmy.ml/api/v3/comment/list?post_id=21766749' | jq '.comments.[] | .comment.content[:50]'
"Yeah, you're right. I didn't read enough of the do"
"Thank you for the tip ... but whatever I try with "
"~~In 0.19.5, they removed the deprecated `post_id`"

I think it would be better to ask the admin of the instance before creating the issue.

I think GET /api/v3/resolve_object should work:

curl --url-query q=https://feddit.org/post/2401677 \
    https://lemmy.ml/api/v3/resolve_object \
    | jq .

(note that the value of q is url-encoded by --url-query)

You can get 50 items at most with limit=50. Try

https://lemmy.ml/feeds/c/lemmy_support.xml?sort=New&limit=50

Not a direct solution but GET /api/v3/site may help.

Maybe some rules in nginx.conf has been delegated to nginx-internal.conf.