I used Godot for this one, and I haven't done a leaderboard in Unity before.
If it helps, I used Supabase for this and its pretty straightforward, and it has a unity plugin that you can use.
If you want something that might be a bit more simple, I have used Talo in the past and its already got most features set up for leaderboards, and they have really good documentation.
Sorry I couldn't be more helpful!