My best guess is you have a lot of apps that open on startup that might be the issue but when you have more ram, you pc naturally allocates more ram to the OS to ensure smooth functionality, for example when I upgrade from 8 - 16 GB macOS went from using 4 GBto 6 GB maybe thats why? Also it could be some app using high memory like video/ photo editor. These are guesses at best tho
Unused RAM is wasted RAM. macOS (and Windows for that matter) allocate a set amount of RAM to itself in order to run smoothly. Windows usually allocates half, whilst macOS 2-8GB depending on the amount of available RAM.
If your usage needs the 24GB, macOS will notice and allocate less RAM for itself.
Again, unused RAM is wasted RAM.
No problem unused ram is wasted ram
There’s nothing wrong your RAM isn’t “gone”
Worry about “Memory Pressure”. Green = Good