You will be issued a gov't laptop. Mine (2018) is a dell, I think '20 got a hp. It most likely will be different than the previous classes'. You're not going to get a top of the line computer with all the bells and whistles, but it won't be crappy either.
Personal computers cannot connect to the ethernet internet in the hall, nor can they access the wifi in the academic buildings. Every company has a wardroom with a civilian WiFi set up, so you can go in there (IF you're not a plebe) and hook up a personal computer or an xbox or an ipad or whatever. The Supe promised that WiFi would be installed throughout the entirety of Bancroft in the near future, but I'm not sure if it'll be the military USNA wifi (and therefore restricted) or civilian WiFi.
You can use your issued laptop for almost whatever you would want to as long as it's legal. You can't download games off of steam on the USNA internet, but you can off of the wardroom Wifi and play them offline on your computer. The bandwidth is such that most video streaming services like Netflix or Amazon Prime tend to run pretty well. They do block some websites but it's things like gambling and porn and stuff like that. VPN's are strictly forbidden. The wardroom wifi comes with some rules, like not downloading pirated movies or pornography or anything like that. They do monitor those types of things and will sometimes shut the wifi down for everybody and/or give you a conduct offense for misusing the wifi.
At the end of 1/c year, they will remove all of the government/security software that's on the laptop so that you can use it after you graduate.
For what it's worth, I don't know many people who choose to use a personal computer. It's just not very convenient since it wouldn't be able to connect to the intranet. Some people have them, but it's not common.