Learn Portuguese (Portugal): Aquele gato é muito preguiçoso e dorme muito.

In Portuguese, muito is a versatile word. When it comes right before an adjective (like preguiçoso), it acts like "very" to make the adjective stronger. When it comes after a verb (like dorme), it describes how much the action happens, so it translates to "a lot" or "much".

If the cat were female (gata), would muito change to muita?

No! When muito is used as an adverb of degree (meaning "very" or "a lot"), it never changes form. It stays exactly the same whether the subject is masculine, feminine, singular, or plural. You would say a gata é muito preguiçosa. It only changes to muita or muitos when it means "many" or "a lot of" right before a noun.

Why does the sentence use é instead of está for being lazy?

We use é (from the verb ser) for permanent traits and characteristics. By saying é muito preguiçoso, we are saying the cat has a lazy personality in general. If we used está (from estar), it would mean the cat is just acting lazy or feeling sluggish right now as a temporary state.

Why use aquele for "that cat" instead of esse?