There are several models of silent keyboards nowadays with technologies, such as “soft touch”, “Cherry Mix”, or even silicone keyboards.
The problem, if you go on Youtube to check the tests of these keyboards is that their cost is very expensive, easily 150 dollars and they are not so silent, compared to the conventional computer keyboards.
The silicone keyboard is actually very silent but the reaction time is very long and the touch sensation is more than bad.
Another solution is to add silicone circles between the keys and the base of the keyboard. For having tested silicone orings, bought 5 dollars in China, I can confirm that it does not work or just a little, the sound is removed by 10-15% at the maximum.
In fact, you have to analyze your keyboard, the noisiest keys are the big keys. If you disassemble them, you will see that there are metal rods that spread sounds like cymbals.
It is therefore necessary to surround their extremities with transparent or brown tape. And there you will see that the sound produced by the keyboard is already much less.