I think it’s called the Title Tag, though it’s for a page, not the site itself.
I don’t have enough experience with the different themes to tell you how to change it in yours, but there are those in this group who would.
If you can get into the HTML, that’s one way; but there ought to be a way that’s much simpler.
You might want to ask the question specifically so that members of the forum will see it.
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