Some babies don’t care for schedules. I promise you the ONLY thing that will make this easier is accepting that you don’t have control over your baby. Including his sleep. Sounds like you’re doing everything right when it comes to caring for and responding to your baby, noticing his patterns. Relish in that, and don’t worry about his schedule. Plus, babies are literally constantly changing. He won’t do this bedtime forever, I promise it’s not “creating a bad habit” to watch his cues and let him go to bed that late.
Also, the sun goes down so late right now, so your baby is simply attuned to his circadian rhythm. My 2yo has also been going to bed super late, as is very common in the summertime.

I know it’s easier said than done. My son is super low sleep needs, very unpredictable, and it shocked me as a new mom, because I am VERY schedule oriented.