Learn Russian: Кто-нибудь проверил эту якобы достоверную ссылку, или это фейк? - Did anyone check this supposedly reliable link, or is it a fake?

The particle якобы translates closely to 'supposedly' or 'allegedly' and is used to cast doubt on a specific fact or description—in this case, whether the link is actually reliable (достоверную). мол, on the other hand, is generally used to report hearsay or paraphrase what someone else explicitly said (like 'he claimed that...'). Because the speaker is doubting the attribute of the link itself rather than reporting a quote, якобы is the right choice.

Does the particle якобы affect the grammatical case of the words around it?

No, якобы is an invariable particle, meaning it never changes form and does not dictate the case of surrounding words. Here, the phrase эту достоверную ссылку is in the accusative case because it is the direct object of the verb проверил (checked). The particle якобы simply slots in right before the adjective it modifies without altering the grammar.

Why does the sentence use кто-нибудь instead of кто-то?

This is a great refresher on indefinite pronouns. кто-нибудь (anyone) is used when the identity of the person is completely open—you just want to know if any person at all did the action. кто-то (someone) implies that a specific, existing person did it, but their identity is unknown to the speaker. In a broad question like 'Did anyone check...?', кто-нибудь is the natural choice.

How is the word (reliable) formed?