В Java 8 для Linux x64 нет libnpjp2.so?

Плагин Java был удален в Java 8 Update 271.

Из примечаний к выпуску Java 8 Update 271 (8u271):

Removed Feature: Java Plugin is Removed from JDK 8u for Linux, Solaris, and MacOS Platforms
NPAPI is considered to be a vulnerable plugin and has been disabled in many browsers. No browsers currently support Java Plugin, which is NPAPI-based, on Linux, Solaris, and MacOS platforms.

Starting from 8u271, the part of Java Plugin responsible for integration and interaction with a browser (in particular libnpjp2 library) and an associated artifact will not be built and is not part of the JRE distribution on Linux, Solaris, and MacOS platforms.
JDK-8240210 (not public)