In an SBS, wasn't it stated Luffy was a Conqueror's haki specialist? He simply has an affinity for it but didn't get an idea of how to apply it into combat but learned after witnessing Kaido and pondering about it. Similar to his fight against Katakuri where he improved his Observation haki.
With Awakening, I suppose it's simply more difficult and requires extensive training with your own fruit. Luffy saw Doffy and Katakuri use it but hasn't shown that he's got a grasp on the concept but has improved his haki after witnessing someone else display their's as well as train for a few days in regards to armament. I think with awakening the user themselves has to completely understand or master their fruit to that level. Hopefully we'll get an explanation soon.
Rayleigh told Luffy his Conqueror's can't be improved by simply training (atleast not in the way you can for armament or observation) and that it'll get stronger along with the user so I guess it's simply Luffy applying what he's been strengthening throughout his journey from before to post-timeskip after getting an idea of how to do so from Kaido.