The nestable slider element sets each slide to be an li. However it does not set the div containing the list items to be a ul, it leaves it as a div which is semantically incorrect.
You cannot set the nestable slider element to be a ul so you have to set its parent container/block/div to a ul. However this is also semantically incorrect as the ul then contains other divs before you get to the list items. You can see this in the screenshot below. The line is blue is the container holding the nestable slider. There are then 3 divs before you get to the list of slider items. The div with the class splide__list should automatically be a ul rather than a div.
Yes sorry, I’m using a frames card which is set to li.
Surely though as we can set the items in the slider to be list items we need the ability to set the slider to be a ul so for screen readers the html is semantically correct.
For anyone who wants to have the .splide__list element to be an ul element if the slides are li elements, use this in your functions.php of your child theme.
Be careful changing the slider/slides to lists though. just changing the HTML tags won’t be enough, as it will mean some of the attributes that splide adds won’t be valid for that element. We had to change these for the bricksextras slider to allow users to change to using lists without the accessibility issue from splide.