well let's see. 40 years ago i learned assembler on the z80, followed by the 6502, 8086 and 680x0 series. i did forth, basic, fortran, pascal, c, c++ and so on over the decades. i worked with chroot and jail systems long before there was virtualization. i worked with solaris zones and aix lpars before vmware became a thing.

something new will always come along. something new will always replace something old. the world moves on. you learn and move on.

if you really want to know linux. why are you working with ubuntu? if you really want to get deep into how, what and why, you should look into gentoo and build your own kernel, organize your own file system and spend endless hours compiling everything. ;-)