Specifically, you can turn on VoiceOver on Mac with Command+F5.
Windows also has a built-in screen reader called Narrator. On Windows 10 version 1703 or later, you can turn it on with Control+Windows+Enter. As of version 1903, it works reasonably well with Chrome, Edge (both Chromium-based and legacy), and IE. Another popular option on Windows is the open-source NVDA (https://www.nvaccess.org/).
Disclosure: I'm a developer at Microsoft, on the Narrator team, but as usual, I'm posting on my own behalf.