Yeah I've never heard of anyone having a topic for a PhD in History chosen for them. If someone has ended up in that situation they really didn't try hard to find a supervisor.

Typically how this works is you recognise an area where there is a gap, this is typically something that comes up during your MA research, or otherwise something you've been thinking of for a bit before then. You build up a good base knowledge of the historiography surrounding that topic, and then reach out to those working on or around that topic and see if they would be interested in supervising.

Sometimes it's an outright "sorry, no" for a variety of reasons, and usually there is some discussion and debate about how the project will go, "have you thought of this, have you read this, this has already been done but if you approach it from this angle then..." etc. but not outright "you do this project instead".

There are research projects that professors may be looking for help in that are specific, but that's not PhD level. I.e. "I need a summer researcher to go through these coins and look for x, y, z; build a database that filters a, b, c" or whatever. But that's a different area completely.