My Mac system memory consumes lot of space, like 77.85 GB

I'm a little confused by your question: space is not memory; space is the space being either used or available on your hard drive or SSD or disk. That is where the entire system, OS, and associated files are located. That also includes your apps and all of your files, movies, videos, photos, etc. Every time you save something to your Mac HD, it will take up more space - it's like a CD you add a song to.

Memory is commonly referred to as RAM and that is what is used to facilitate opening apps, working in them, browsing the internet, etc. You may have 8, 16, or more GB installed. There is no way that is 77 GB.

So, if you will highlight your Mac HD (that is your hard drive) and hit the Command + i keys, you will get a get info window with the space used and available listed. Please post a screenshot of that.

Also confirm your exact model/year of your device along with the OS version.

Actually the systems memory consumption that you see is the memory taken up by the system and it is combined with documents. I have encountered this problem many times and using a utility called omnidisk sweeper found that my system memory usage is being shown combined with the documents usage for some weird reason. Also apps like android studio show up under system memory and not applications.