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But are there similar services but only for creating exchanges, so that even a schoolboy easily could create his own exchange?
Like @rat03gopoh already said, even if there were such services, who in their right mind would use such an exchange? Would you? Its important to understand that crypto exchanges are holding very large amounts of other peoples money. In many cases, thats billions of dollars!
No, you cant just spin-up a legitimate, operational, and secure crypto exchange with a website builder like making a blog. The reason is simple, a cryptocurrency exchange, either CEX or DEX, is a complex, high-stakes, financial machine - not a hobby project.
So, if you want to do some experimentation with creating a crypto exchange along the lines of the learning journey, look up open source repositories with example projects for crypto exchange and start from there. But if you want a functional and operable exchange, forget about it. This is a serious undertaking that requires an expert team of developers and a mountain of seed money.