@Whatever it looks like the same desert that was used to attempt to poison him when he was a kid.

@Whatever Trump gave Sophie immortality. Trump then dissapeared, but he didn't die hence the "even if he burns to ash, he will exist somewhere in this world". Sophie didn't become the "new Trump". He only became immortal. Minor spoiler but Sophie then vanishes and makes it his mission to find Trump. What he does after leaving Clan is another story, there's a stageplay for it but time will tell if they'll adapt any of the other content.
There's actually one more extra chapter that continues on the last few panels you see (where Sophie is looking out of the window). I'll explain it below, but ofc skip if you don't want spoilers.
Spoilers:
The old man there is Ga Banri's old partner if I remember correctly. He has been looking for Sophie and finally meets him at this funeral at his old age. He's been looking for Sophie to tell him the truth, aka that Ga Banri was his uncle and what had happened that led him to be send to an orphanage. Sophie tells him about his mission to find Trump. The partner can't bring himself to tell Sophie the things he wanted to tell him about, but then does tell him albeit off screen.

@Whatever Sophie is a boy

@Bee he's not his dad.. I won't spoil you further unless you want to