Learn Russian: Всё это не по-настоящему.

It is formed from the adjective настоящий (real). To make adverbs of manner meaning "in a certain way," Russian adds the prefix по- and changes the adjective's ending to its dative case form. For adjectives like настоящий, this dative ending is -ему.

Why doesn't it end in -и like по-русски?

Adjectives ending in -ский, -цкий, or -ьи (like русский) drop their last letter and take the ending -и when combining with the prefix по-. Most other adjectives, including настоящий, use the standard dative endings -ому or -ему to create these adverbs.

Why are Всё and это in the neuter singular form here?

We use the neuter forms всё (everything/all) and это (this) when referring to an abstract situation or a general concept, rather than pointing to a specific noun. Together, Всё это acts as a phrase meaning "All of this" or "This whole situation."

How would you say "All this was not for real" in the past tense?

You would add the neuter past tense verb было to match the neuter subject Всё это. The sentence would become: Всё это было не по-настоящему. In the present tense, as shown in this example, the verb "is" is simply left out.