Learn Dutch: Ondanks de grote inspanning zullen we moeten volhouden. - Despite the great effort, we will have to persevere.

Just like the English word "despite", ondanks is a preposition that directly attaches to a noun phrase. Here it connects directly to de grote inspanning (the great effort) without needing any extra linking words like "of" or "that".

Why is the word order zullen we instead of we zullen?

This is the V2 (verb-second) rule. Because the sentence starts with the phrase Ondanks de grote inspanning, that entire chunk takes up the first position. The conjugated verb zullen must be in the second position, so the subject we is pushed to the third spot.

Why are there two infinitives, moeten and volhouden, at the very end of the sentence?

The verb zullen is an auxiliary (helping) verb, which sends all other verbs to the end of the sentence. Because we are expressing "have to persevere", we end up with two infinitives stacking together. When combining a modal verb like moeten and a main verb like volhouden at the end, the modal usually comes first.

Volhouden is a separable verb. Why isn't it split up here?