Why, in 2021, does anyone need to learn about assembly language? First, reading assembly language is the way to know exactly what your program is doing. Why, exactly, is that C++ program 1 MiB (say) instead of 100 KiB? Is it possible to squeeze some more performance out of that function that gets called all the time? For C++ in particular, it is easy to forget or just not notice some operation (e.
Today i think that assembly is used mostly for programming micro-controllers or to increase performance of certain things that require fast calculation but would be too heavy if programmed in an high level language.
Compilers have settings for optimization (look at the g++ manual for instance).
I would suggest to know at least the basics of how an assembly language operates because it teaches you how to write optimized code (especially if you work with languages like c that are high level but still close to the machine)