Learn Spanish (Latin America): Lo de maullar y ronronear mucho es normal. - The thing about meowing and purring a lot is normal.

Lo de is a neuter phrase used to refer to a general situation, matter, or topic rather than a specific masculine or feminine noun. In this sentence, it neatly packages the entire concept of the cat's behavior, translating roughly to "the matter of" or "the thing about" meowing and purring.

The English translation says "meowing and purring", but the Spanish uses the infinitives maullar and ronronear. Why not use the -ando or -iendo forms?

In Spanish, when a verb functions as a noun (such as the object of the preposition de in this sentence), you must use the infinitive. The gerund forms like maullando and ronroneando are strictly used for continuous actions in progress, such as "the cat is meowing" (el gato está maullando).

Does mucho ever change its ending here to match a gender or number?

No, it stays exactly as mucho. In this sentence, it is acting as an adverb modifying the verbs maullar and ronronear to mean "purring a lot." Adverbs are invariable, meaning they never change form. It would only change to mucha or muchos if it were an adjective describing a specific noun.

There are two activities mentioned (maullar and ronronear). Why is the main verb singular () instead of plural ()?