Is Gutenberg for WordPress Accessible?

Unfortunately, the short answer is, no, Gutenberg is not really accessible.

This is my understanding from the Report on the accessibility status of Gutenberg post on wordpress.org.

For a new method of editing, it seems quite shocking that accessibility, in this day and age, has not been a major consideration from the start. Showing how dire the situation is, Rian Rietveld, the accessibility team lead, has resigned.

The only real recommendation is to revert back to the current standard experience, by installing the Classic Editor, but this has been announced as only supported until 31^stDecember 2021. After this the Classic Editor will no longer be supported.