Interestingly it takes up 400 mb ram whereas messages takes up 610, which I find confusing

Because you pay for access on your cable provider, like you would pay for your internet on your internet provider. Then you can watch free channels or pay for certain channels, like you would pay for Netflix or Disney+ or whatever is called. With the paid services there shouldn't be any ad, with the free services like YouTube, you get ads so YouTube can pay their bills.

So, you analogy was completely missing the point and is not comparable to a paid operating system. You don't even get ads with free operating systems, or with your paid competitor Apple.

Any allocations done by the library running (opencl.so in this example) will still be separate per process though, unless the program is passing mutable shared memory buffers around, which could be the case if there's IPC going on.

The point about memory usage being hard to measure is definitely true, especially since linux won't actually consume memory until a write is made to the block, unlike Windows which preemptively allocates the full requested size.

When a program loads a .so a version of that file is loaded in the program's virtual memory space so technically that same .so file exists in multiple virtual spaces, but that's only a trick used by your MMU (memory management unit), the .so file is only loaded once in actual memory:

Let's imagine some program loads opencl.so and no one else on the system uses it. The kernel will check all needed libs and loads that one at physical address 0x700. After loading it up it talks to the MMU and creates a virtual address space for said program, telling the hardware to create a read-only link between virtual address 0x100 and physical address 0x700, "loading" the library in virtual memory (without actually making a copy). If some other program then needs opencl.so the kernel will recognize that lib as already loaded so skips ahead to linking virtual adress 0x200 (or whatever really, virtual address space is specific to one instance of one program, it could be 0x100 again it doesn't matter) to physical address 0x700, once again loading it in program memory without making a copy.

You could argue some optimization would benefit it, but at 247MB with an OS that is good at managing memory, I really don’t see how much smaller you could get it to.

When a program loads a shared library, it creates a new instance of it that runs in the same memory space as the program.

In the example you're using with KDE, that's actually a system process that your program is communicating with, so it's not quite the same as just loading a shared library (.so).
Since new programs can connect to the existing system service, that can end up saving RAM by having a single system program service multiple user applications.

This isn't really any different on Windows where the desktop environment (dwm.exe) is handling drawings and compositing for all user apps.

Edit: Based on the downvotes, maybe I got something wrong here. Maybe someone can comment on what? I'm happy to learn

I forgot about the ads.

As an example, if I already run KDE on my system and another KDE app starts up, it might not use too much more RAM. But the same app on a GNOME system might require a lot of additional RAM. So the Windows 11 Weather app might not even use 1.2gb on its own. No idea how they measured it.