Legally the laptop would belong to John Paul Mac Isaac per Delaware's Abandoned Personal Property laws (25 Del. C. § 4001). He would have a right to ownership of the laptop. That said, the data contents of the laptop should have been wiped (that's customary, not a legal requirement) before the transferring of ownership.

All of that said, 18 USC § 1030 covers the data that is hidden behind a Windows login. Yes you can boot up a system with an unencrypted drive and read the contents of it, but that's circumventing. Now where this and everything else differs, is that in a lot of prior cases a warrant was obtained to gain discovery of the information. In this case, Giuliani just circumvented the login, and post facto indicated evidentiary data.

It's a good question to bring before the courts. Can someone circumvent a protection, find incriminating data, and then after the fact present it to law enforcement? Because we don't have a lot that goes down this road of questioning. Kind of the reason law enforcement needs to be the one that bypasses those kinds of protections legally is because, your average person, can do things that "tamper" with evidence. And with digital data, can do so without knowing they have done so, like last access timestamps and what not.

and if so, how is that not illegal access to someone else’s data

I mean that's the central question of the suit. Which you can find as case 2:23-cv-8032 in the Central District of California. And I can't off the cuff think of a good prior that answers this. And there's parallels that can be drawn for both ways this can go. You cannot just randomly break into a house, discover illegal shit going on, and then report that (I mean you can, but you've also violated the law with your B&E) But if you reasonably suspect something is going on (like you heard a scream from the house), you can break into a house, discover illegal shit going on, and then report that (that is you haven't violated the law with your B&E in some situations).

Basically the case doesn't negate the laptop as evidence in some other case, it just implicates Giuliani into what amounts to digital breaking and entry. Which given the case, even if Giuliani was found guilty the sentence is usually a fine for first offense when the information obtained is not property of the US Government proper. So even if the courts do find Giuliani should have contacted the FBI before actually attempting to get the data, the most he would be face (if they really wanted to throw the book at him) is one year in prison AND a fine.

It is an interesting case though, we don't have laptops screaming for help to justify breaking legally protected locks on data. So, it an interesting case to see what the courts lay down as lines for "reasonable belief that an illegal activity is happening" if Giuliani decides to go down that road. But I don't hold much hope for that, they'll likely argue that the data on the laptop is theirs to begin with, which no court is going to accept that. But we'll just have to see.