The best way to learn about the current state of things is to try and build something.
You could start with something affordable, like a KBD67 Lite kit. You'll separately need switches, keycaps, and maybe stabilizers and a custom coil. You'll want to customize your switches. Just the effort of doing that will quickly introduce you to a lot of elements.
In terms of reading, visit the Deskthority Wiki, which contains a lot of information about historical keyboards, and the concepts and terms used. If you also search on this forum about switch customization, such as building Ergo Clears, "Ghost Blacks," and how MX Brown, Clear, and other basic switches were once considered exotic, you will learn a lot about what came past.
Getting involved in Group Buys will teach you a lot about the process. You could start with something modest like ePBT or JTK, or something even cheaper like Infinikey. Or GrayStudio, as they produce some affordable items.
You can read reddit/r/mechanicalkeyboards for a lot of photos, there's here and keebtalk where discussion takes place. There are popular Youtube channels like Chyrosan22 and Glarses. And if you go onto Discord, there is enormous chatter in several Discords.