Learn Turkish: Onlar bu kandırmacayı uydurmuş olabilir. - They might have fabricated this hoax.

The structure uydurmuş olabilir is the positive possibility form, meaning "might have fabricated". It uses the past participle -mış followed by the possibility auxiliary olabilir. To make the strong negative deduction taught in this lesson ("cannot have fabricated"), you simply swap olabilir for olamaz, giving you uydurmuş olamaz.

Since the subject is Onlar, why doesn't the verb have a plural suffix like olabilirler?

When a third-person plural subject is explicitly stated with a pronoun like Onlar (or refers to humans), adding the plural suffix -lar or -ler to the verb is optional. Using the singular form olabilir here is completely grammatically correct and sounds very natural.

Why does the word kandırmaca take the -yı suffix here?

The word kandırmaca (hoax or deception) is the direct object of the verb uydurmak (to fabricate). Because it is preceded by the demonstrative adjective bu (this), it is a specific object, so it must take the specific accusative case suffix -(y)ı.

How is the noun kandırmaca formed?

The root is the verb kandırmak, which means "to deceive" or "to fool". Adding the suffix -maca turns a verb into a noun that describes an act, game, or concept (similar to how bulmak becomes bulmaca, meaning "puzzle"). Therefore, kandırmaca means a "deception" or "hoax".

Does uydurmak always mean "to fabricate" or "to make up"?