MuZero performs a "formal search". In many more ways than one, for example optimisation is still a search for an optimal search of parameters. But I guess you mean that it doesn't perform a tree search? Quoting from the abstract of the paper on arxiv [1]:
In this work we present the MuZero algorithm which, by combining _a tree-based search_ with a learned model, achieves superhuman performance in a range of challenging and visually complex domains, withoutany knowledge of their underlying dynamics.
(My underlining)
If I remember correctly, MuZero is model-free in the sense that it learns its own evaluation function and reward policy etc (also going by the abstract). But it retains MCTS.
Indeed, it wouldn't really make sense to drop MCTS from the architecture of a system designed to play games. I mean, it would be really hard to justify discarding a component that is well known to work and work well, both from an engineering and a scientific point of view.
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https://arxiv.org/abs/1911.08265
