Java 8 has commercial features that are locked by default. You can unlock them by passing a command line flag that looks like -XX:+UnlockCommercialFeatures, so pretty hard to miss.
If you use those in production, you're meant to pay. But virtually nobody does use them. In fact Oracle open sourced them all for Java 11, perhaps because of that fact.
Now in Java 11 there are two JDKs, that are virtually identical. OpenJDK and Oracle JDK. The latter is the same as the former but commercially supported. If you use it in production at all, you're meant to pay. But the only reason to do that is you want commercial support, from what I understand. There are no longer any special features. If you can support yourself (like most can) you just switch to OpenJDK as part of your Java 11 upgrade.
They have not changed the license for Java 8 users "on the fly", I'm not even sure that's legally possible.