Selenium uses a chatty HTTP interface, whereas puppeteer/playwright use WebSockets or pipes to communicate. Under-the-hood, however, Selenium is simply using chrome's devtools protocol to communicate with it. The way selenium does this is by another binary, generally a `driver`, that has the protocol "baked" into it and has the HTTP selenium API as its input interface.
This is all a long way of saying that puppeteer/playwright have a lot less moving parts, and are generally more approachable. Selenium _does_ have a lot more history behind it, better support across languages and frameworks, and is more stable but it's also much larger and "clunkier" feeling. It's also a lot harder to scale with load-balancers since, again, it's all over HTTP so you'll need some way to load-balance with sticky sessions.
Practically speaking they all do the same thing at some layer. Both are high-level APIs around the devtools protocol, it's just what higher-level interface you prefer and what your language/runtime is.