1. Remove the ImageMagick module - it is not compatible with the recently rewritten image system of thirty bees. Nobody should use this module since thirty bees 1.5 version as it gives no benefits in 2025.
2. Configure webp or avif in Images as you did before and again regenerate all image thumbnails. As you see in this section thirty bees core is responsible for the images for manufacturers, products, scenes, categories, etc. Not for the module images - slider, blog, etc modules have their inner way of handling those and sometimes they are not compatible with webp or avif.
3. The slider module should be modified to support webp and avif and the modification i fairly simple. Look at the code. Soon this will be fixed in the codebase but the developer is currently working on other more pressing issues. Keep in mind you should add prepared and properly sized images here as the module simply stores them and shows them to the FO, it does not do any processing.
Cheers!