Can a MacBook get hacked through WiFi?

Your Mac's login name and password protect it from unauthorized intrusion. No one and no thing can access it without those credentials. Following these steps will ensure the security of your Mac: Set up your Mac to be secure - Apple Support.

Your iCloud Account is similarly protected with your Apple ID credentials. Keep them secure as well: Keep your Apple ID secure - Apple Support.

Regarding your question about Wi-Fi specifically: there are no additional precautions necessary to keeping your Mac or your Apple ID secure — however — if you are using a public Wi-Fi network the possibility exists that any unencrypted network traffic can be intercepted. You should proceed on the assumption that it is being intercepted. The unencrypted part is important though, because there are almost no websites that do not use encryption. Any website that engages in commerce (Amazon et al) use encryption. Banking sites use encryption. And so on. Even this site uses encryption. So even if you are using an "open" Wi-Fi network, any traffic that gets intercepted will be indecipherable. Passwords are encrypted. Everything is encrypted. In that limited regard there are few if any distinguishing characteristics between "open" Wi-Fi networks and "captive" networks that only permit communication between devices logged into it.

But the bottom line is this: there are no ways of "hacking" into a Mac by circumventing the login name and password that you use to log in. Once logged in though, whoever is logged in might as well be you. The Mac can't tell the difference. So keep those credentials to yourself, and make sure no one is looking over your shoulder (literally or figuratively) when typing them in. Same goes for iPhones. That really is the weakest link in the security chain. So go ahead and take care of your banking business, your credit card business, etc. Just be aware of your surroundings, as anyone should.