You need to install OpenJDK 8 or 11. Use a portable version of Java (like Liberica JDK) on your USB drive and point your launcher to that path.
: A web-based port of Minecraft (usually version 1.5.2 or 1.8.8) that runs directly in a browser. While it isn't native 1.16, many servers hosted on it use plugins to mimic 1.16 features or allow players to join 1.16 servers. Minecraft Classic Minecraft Unblocked 1.16
Even with a good unblocked source, you may hit snags. You need to install OpenJDK 8 or 11