Install a different system monitor. That's the beauty of Linux. You don't need to use Cinnamon, Gnome, KDE, or whatever.

Windows is also using mebibytes. It just mislabels them as megabytes.
That's why a 1 TB disk is shown as 931 GB in Windows.

Many modern tiny operating systems still could fit in one single 3.5 inch floppy disk.
They have multitasking, GUI, ethernet support, and could run 3D games.
No. I am not joking.

But major operating systems have compatibility burden, and have to support tens of thousands of different hardwares.
Strip down those drivers that you do not need, will make Windows, macOS, Linux much much smaller.

Microsoft tried to make Windows 10 smaller, and you guess what? Many games could not run on it, and gamers are angry about it.

The thing is - what was called KB and MB back then was what we know as KiB and MiB today.

Since the new definition really only applies to storage and because of the less-than-honest marketing drive makers have been employing in the past twenty years or so, I think the big reason the definition was changed is because the drive makers wanted to be able to claim to have larger drives.

I just ignore all of that nonsense. To me a kilobyte will always be 1024 bytes, which is still the commonly preferred method that RAM and networking speeds are calculated.

The mebibyte is a multiple of the unit byte for digital information.[1] The binary prefix mebi means 220; therefore one mebibyte is equal to 1048576bytes = 1024 kibibytes. The unit symbol for the mebibyte is MiB. Technically a megabyte (MB) is a power of ten, while a mebibyte (MiB) is a power of two, appropriate for binary machines.

The unit was established by the International Electrotechnical Commission (IEC) in 1998.[2] It was designed to replace the megabyte when used in the binary sense to mean 220 bytes, which conflicts with the definition of the prefix mega in the International System of Units (SI) as a multiplier of 106.

The binary prefixes have been accepted by all major standards organizations and are part of the International System of Quantities.[3] Many Linux distributions use the unit, but it is not widely acknowledged within the industry or media.[4][5][6][7]

https://en.wikipedia.org/wiki/Mebibyte

yeah, why are OSes so stupidly big? I mean, really? Is it all just spyware?

I'm not sure what OSes you're using, but most Linux distros can be crammed into a standard CD still, if not even less.

I wanna use Mebibytes now :D