Since not only … but also is a correlative conjunction, there is no exact synonym. However, instead of using not only … but also, you could rewrite the sentence to use a conjunctive adverb such as “moreover” or “furthermore” instead.
Not only … but also synonym examples
He not only won the election but also won by a landslide.
He won the election; moreover, he won by a landslide.
He won the election; furthermore, he won by a landslide.
The QuillBot Paraphraser can help you rewrite sentences and find alternative ways to express your meaning.