Peer-review policies vary for journal publishers. Journal content such as book reviews, letters to the editor, and opinion articles may or may not be peer reviewed.
For example, the peer-review policy of Nature Portfolio journals states "The following types of contribution to Nature Portfolio journals are peer-reviewed: Articles, Letters, Brief Communications, Matters Arising, Technical Reports, Analysis, Resources, Reviews, Perspectives and Insight articles. Correspondence and all forms of published correction may also be peer-reviewed at the discretion of the editors. Other contributed articles are not usually peer-reviewed."
Peer-Review Policy. Springer Nature, 2021, www.nature.com/nature-research/editorial-policies/peer-review. Accessed 18 Mar. 2021.