Learn French: Qu'il reste craintif est normal avant de l'apprivoiser. - That he remains fearful is normal before taming him.

It is in the subjunctive. When a sentence starts with a Que clause acting as the subject (meaning 'That...' or 'The fact that...'), the verb in that clause must always be in the subjunctive. Even though the indicative and subjunctive forms of regular -er verbs like rester look identical for il, the rule demands the subjunctive here.

Could I say Le fait qu'il reste craintif instead of just Qu'il reste craintif?

Yes, absolutely! Starting a sentence with just Que + subjunctive is a bit more formal and elegant. In everyday spoken French, people often prefer to use Le fait que or rephrase the sentence entirely (for example, C'est normal qu'il reste craintif).

Why do we use avant de + infinitive instead of avant que + subjunctive here?

Avant de is followed by an infinitive and is used when the statement is general, or when the subject of both actions is the same. Because this sentence is a general statement about taming an animal, the infinitive l'apprivoiser is the most natural choice. If you wanted to specify exactly who is doing the taming, you would need avant que + subjunctive (for example, avant que tu ne l'apprivoises).

Does apprivoiser just mean to domesticate an animal?