Learn Russian: Это музей компьютеров.

This is the genitive plural form, which we use to mean "of computers." Because компьютер is a masculine noun that ends in a hard consonant (р), it takes the -ов ending in the genitive plural. The phrase literally translates to "a museum of computers."

In English, we say "computer museum." Why doesn't Russian use an adjective for "computer" here?

Russian very often uses a "Noun + Noun (in the Genitive case)" structure instead of turning the first word into an adjective. While you could technically use the adjective form (компьютерный музей), saying музей компьютеров (museum of computers) is the most standard and natural way to express this in Russian.

Why doesn't the word это change to masculine to match музей?

When это is used as a standalone subject meaning "this is" or "that is," it always stays in this fixed, neutral form. It doesn't matter if the noun that follows is masculine like музей, feminine, or plural.

What does the soft sign (ь) do in the middle of компьютеров?

Here, it acts as a separating soft sign. It stops the consonant п from blending directly into the vowel ю. It creates a slight separation so you hear a distinct "y" sound, making it sound like "komp-yu-ter" rather than squishing the п and ю together into a single syllable.