For a typical desktop Linux 12 GiB should be fine.

It depends on what you do with the system, of course. If you regularly compile big and template-heavy C++ codebases, work with Blender,… then 12 GiB won’t be enough.

(What really surprised me was how much can still be done with just 4 GiB of memory. My laptop is currently limited to 4 GiB, and with some effort to set up a minimalist system it’s working surprisingly well. I barely ever hit the memory limit - actually only when compiling big template-heavy C++ codebases 😉.)