Reactionary personalities are amongst the most difficult to work with. In businesses we usually just fire them, regardless of their technical competency -because their personality gets in the way and they are not efficient anymore, and their technical competency goes to waste, since most work is strongly collaborative.

But a PhD is not your ordinary professional collaboration.

Is doing a PhD seen relatively more as a personal journey (of the student) with a map/compass (the supervisor)? Or is it seen relatively more as a production line of capital goods, where the student is the capital good under construction (designed and destined to be productive itself at a later date), while the supervisor is the manager of the production line, which in turn is part of the factory/University?

It matters how you see it but also how your institution sees it.

If the latter, find a a way to fire them in an appropriate way, and other answers suggested various such approaches.

But if the former, you are the map, you are the compass, not the captain of the ship. A probably useful approach in this case would be to demand (not just ask) from the student to come up with and justify and argue in favor of, their own project idea, if they don't like what you propose. They have to learn, or acknowledge, that if they want to be "their own person", they are obliged to shoulder the responsibility and the heavy burden, that comes with it. This also will put to the test their knowledge and ideas-generating potential.

And then, you will have objective grounds for assessment: if they propose something that you don't consider worthy, you have every legitimate reason to finish the collaboration. But you may like what you see, and then, maybe it will worth the trouble.

Reactionary personalities are amongst the most difficult to work with. In businesses we usually just fire them, regardless of their technical competency -because their personality gets in the way and they are not efficient anymore, and their technical competency goes to waste, since most work is strongly collaborative.

But a PhD is not your ordinary professional collaboration.

Is doing a PhD seen relatively more as a personal journey (of the student) with a map/compass (the supervisor)? Or is it seen relatively more as a production line of capital goods, where the student is the capital good under construction (designed and destined to be productive itself at a later date), while the supervisor is the manager of the production line, which in turn is part of the factory/University?

It matters how you see it but also how your institution sees it.

If the latter, find a a way to fire them in an appropriate way, and other answers suggested various such approaches.

But if the former, you are the map, you are the compass, not the captain of the ship. A probably useful approach in this case would be to demand (not just ask) from the student to come up with and justify and argue in favor of, their own project idea, if they don't like what you propose. They have to learn, or acknowledge, that if they want to be "their own person", they are obliged to shoulder the responsibility and the heavy burden, that comes with it. This also will put to the test their knowledge and ideas-generating potential.

And then, you will have objective grounds for assessment: if they propose something that you don't consider worthy, you have every legitimate reason to finish the collaboration. But you may like what you see, and then, maybe it will be worth the trouble.