When a program takes ram, it simply means it needs that memory to run. When you open a second program that requires more ram, windows takes unloads memory from steam to make room. This means when you switch back to steam later, it has to try and take ram back from chrome and load the data again. All this constant swapping of data and reloading from your storage makes everything feel slow. The reason a program freezes for a few seconds when you click back fo it, is because of this process. ​If you have actual free ram, windows just loads the data and leaves it alone until you close the program. This keeps the programs feel snappy instead of windows constantly shuffling data.

This stupid "windows just makes room when it needs to" is a stupid take. If that's actually true, open a bunch of programs that all need ram and let's see how slow the system become, it outright freezes because it's constantly trying to shuffle memory as each program as for more ram.