Is ambiguous cfg(context free grammar) more expressive than unambiguous cfg?

Question

I found that the following ambiguous cfg can not expressed by unambiguous cfg:

S → a S B | x
B → a | ε

such as: aaxa: S → a S B → a a S B B → a a x B B → a a x ε B or a a x B ε

I tried to ask for chat gpt ,but it gives me wrong answer. And I can not convert it to unambiguous grammar by known method