Learn Hardcore Japanese: atarasii sakusen no okage de sigoto no kouritu ga agarimasita. - Thanks to the new strategy, work efficiency improved.

The の is the genitive/attributive particle that links two nouns. Here it turns 作戦 (“strategy”) into an attributive modifier of おかげ (“thanks, credit”). Together they form the set expression Xのおかげで meaning “thanks to X, ….”

What exactly does おかげで mean and how is it used?

おかげで is a fixed pattern meaning “thanks to” or “as a result of (in a positive sense).”
• You attach の to a noun (or noun phrase) and then で.
• It introduces a positive cause or reason for something good happening.
• Example: 天気のおかげで “thanks to the weather…”

Can I replace おかげで with せいで in this sentence?

Grammatically yes, but semantically no.
• おかげで conveys a positive result.
• せいで also means “because of,” but carries a negative nuance (“unfortunately,” “due to someone’s fault”).
Using せいで here would sound like you’re blaming the new strategy for some negative outcome.

Why is 効率 marked with が rather than を or は?