In layman terms, these buttons and links need to be somehow labelled so that screen readers can discern the purpose of the link/button and then relay that to the user. One way to do that is by giving the buttons an aria-label attribute, for example:
Note that without the aria-label the computer would somehow have to figure out that a button with the text X means close (modern screen readers or even other accessibility softwares haven’t come this far yet), by adding the aria-label attribute you should be able to improve accessibility and fulfill the suggestion given by Google.
As an example for the button with the search icon:
Note this is an example your search button may look different.