user17004: A similar question was posted in the past (2020):
Is there a way on lichess to see the Correspondence chess rankings?
However, that solution is not working anymore. In my perspective, things have changed and lichess.org is allowing correspondence chess, but a ranking does not exist anymore. Is there a way to be certain about this topic?
Also, why lichess.org is treating correspondence chess differently, if that is the case? I am guessing  that is difficult to control who is cheating and who is not. In the past I used to play correspondence chess, but I am playing classic games now. According lichess.org classic are games that each side has 30 minutes or more for the entire game. Correspondence chess you have 1 day per move or more. Chess.com calls correspondence daily chess.

user9179: Although it's from six years ago, the lack of leaderboards for correspondence chess in lichess was explained by its creator in this reddit post.
Quoting from reddit's user ornicar2 (who is labeled as lichess creator):
"We don't have correspondence leaderboards because it's impossible to accurately monitor for cheating. While player behaviors are analyzable and somehow predictable in timed games, go figure what happens when a player spends 24h between two moves."

17004: <p>A similar question was posted in the past (2020):<br />
<a href="https://chess.stackexchange.com/questions/27889/is-there-a-way-on-lichess-to-see-the-correspondence-chess-rankings">Is there a way on lichess to see the Correspondence chess rankings?</a></p>
<p>However, that solution is not working anymore. In my perspective, things have changed and lichess.org is allowing correspondence chess, but a ranking does not exist anymore. Is there a way to be certain about this topic?</p>
<p>Also, why lichess.org is treating correspondence chess differently, if that is the case? I am guessing  that is difficult to control who is cheating and who is not. In the past I used to play correspondence chess, but I am playing classic games now. According lichess.org classic are games that each side has 30 minutes or more for the entire game. Correspondence chess you have 1 day per move or more. Chess.com calls correspondence daily chess.</p>
 9179: <p>Although it's from six years ago, the lack of leaderboards for correspondence chess in lichess was explained by its creator in <a href="https://www.reddit.com/r/chess/comments/3zfrhq/on_lichess_why_people_doesnt_seem_to_be/" rel="nofollow noreferrer">this reddit post</a>.</p>
<p>Quoting from reddit's user ornicar2 (who is labeled as lichess creator):</p>
<p>&quot;We don't have correspondence leaderboards because it's impossible to accurately monitor for cheating. While player behaviors are analyzable and somehow predictable in timed games, go figure what happens when a player spends 24h between two moves.&quot;</p>
