Microsoft Office comes in several flavours. You can still buy a license for one PC. However, Microsoft would like you to buy a subscription.
The single PC license still exits. It lets you use the Office applications on one PC. That's it. If your PC ends it's life so does your license. This is how many people used Office applications at home. They bought a copy of Office, usually at a discount, when they bought a PC. It got to the point where retailers just added in the cost and people assumed that Office applications were part of Windows. That was both good and bad. If consumers kept their PC for 5 years they never paid Microsoft any more cash. They also didn't get any enhancements from later versions. Suddenly they might get an Excel spreadsheet or a Word file with gibberish in the middle. A sign that a later version inserted a new type of data.
A single PC license would cost quite a bit but it lasted for years. Students got lower prices that hooked them in to Office applications whether they used a PC or a Mac. Office across different devices became a larger business than Windows itself as the PC market declined and mobile devices took centre stage.
Microsoft would prefer you bought a subscription. The subscription model is now branded Microsoft 365 Family. For a fixed monthly or annual fee you can have Office software for multiple people in your family for multiple devices with a large amount of cloud storage. The price over three or four years across the 6 permitted users and devices is significantly less the old model of upfront cash. You also get continuous upgrades and security updates. If you shop around on websites that highlight deals you can buy at an even cheaper rate.
However, what if you really don't have much money? What if you rarely need a productivity application suite like Office? There is a way of getting Office for free. It's not all of the Office suite you can pay for but it's free. If you have a Microsoft Account (MSA) then you can go to Office.com and login for the web based version of Office. You may already have a Microsoft Account. Its any email address for outlook.com, hotmail.com, msn.com or any other of the Microsoft services. You get a 15gb Onedrive space to store your documents and web access. Its what Google offer with docs and drive. The difference being you can create and use Office like paying customers.
Consumers often don't realise there is a free option for Office. There is. For most people it may be all you need.