The answer to this questions depends a lot on another question: what kind of designer do you want to be? After 15 years in the industry I can tell you that the "Mac standard" is long gone. Many of us still prefer Macs but most of the better agencies I've worked at gave me some choice on the hardware I wanted to use. If you can afford it, Apple makes great hardware and software. We currently have 4 Macs in our house (sold a few as well) and they're all running great, even the 2006 iMac.
If you're a "traditional" graphic designer that works mostly on print or branding you could use whatever you like. Adobe Creative Cloud is cross-platform. Thanks to OpenType most of the font issues from previous versions of Windows are no longer common. Even newer programs like Affinity Designer and Affinity Photo are now available for Windows.
A lot of smaller agencies have switched away from Final Cut Pro. That means you no longer need to work from a Mac for motion and video work. You may even be better served with a PC since you have more options for graphics cards and upgrades to improve performance.
This is where I would tell you to buy a Mac. Our agency is about 80% digital projects (web apps, websites and mobile apps) and I spend most of my day in Sketch. You may also find yourself needing to use prototyping apps like Origami Studio (Mac only), Framer (Mac only) or Flinto (Mac only). Besides these tools, Macs also provide a full unix-like environment which makes frontend development much easier and more productive. The "should designers code?" question has been asked a million times but if you learn to write basic code it will only help your career as a digital designer.