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Uh, memory metrics in Linux are a pain. The only tool that reports most cached as available is htop. free, top and a lot of other software (like node_exporter) will report that a lot of cached memory is not available.
To OP: don’t worry, a lot of Linux tools are smart enough to give back memory if memory pressure rises.
Counter-counter point: people don’t get a Mac or windows laptop to learn about osx or windows. They generally want to run software or at least browser to do what they need to do.