What has the author T Muir written?

You're likely thinking of Tamsyn Muir, a fantasy author known for her Locked Tomb series. Here are the books she has written:

* Gideon the Ninth (2019)

* Harrow the Ninth (2020)

* Nona the Ninth (2022)

She is also writing Alecto the Ninth, the fourth book in the series.

It's important to note that there are other authors with similar names, so specifying "Tamsyn Muir" helps to avoid confusion.