The block mover buttons are empty, there's no text or aria-label at all, thus there's nothing that can be announced by assistive technologies.
For screen readers, they could use hidden text or an aria-label. I'd recommend to test them also with speech recognition software, really not sure how they can be activated if they have no visible text at all.

Additionally, the color contrast is really low. As a reminder, the WCAG level AA WordPress aims for requires a color contrast ratio of at least 4.5:1.

About the SVG icons, see the specific issue #528

Of course, these buttons should be fully operable when using only a keyboard.