The tabindex global attribute indicates that its element can be focused, and where it participates in sequential keyboard navigation (usually with the Tab key, hence the name).
<p>Click anywhere in this pane, then try tabbing through the elements.</p>
<label>First in tab order:<input type="text"></label>
<div tabindex="0">Tabbable due to tabindex.</div>
<div>Not tabbable: no tabindex.</div>
<label>Third in tab order:<input type="text"></label>
Sources:
https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/tabindex
https://www.freecodecamp.org/learn/responsive-web-design/applied-accessibility/use-tabindex-to-add-keyboard-focus-to-an-element