Hi @Illarion,
Thank you for being so patient,
After further investigation, it turns out that the accessibility issues you mentioned (the focusable descendants in elements with aria-hidden="true" and the invalid ARIA role) are caused by Splide, the library we use for the Nestable Slider element. Unfortunately, both of these issues are outside of our direct control.
We recommend reporting these issues directly to Splide through their GitHub repository: Issues · Splidejs/splide · GitHub. In fact, the second issue regarding the ARIA roles already has an open issue on their tracker: Lighthouse Accessibility warning · Issue #1241 · Splidejs/splide · GitHub.
Thanks again for your understanding.