Ok here’s what’s going on. You probably have some lists with tons of items in them, like thousand+
This TestFlight implemented some basic optimization so Clear can now handle extremely long lists without crashing. However there is going to be more work to do in updates to further optimize performance.
For the time being:
If the thousands of items in these lists happen to be crossed off items you haven’t cleared, and you do not need those saved, go ahead and possibly break the record for the most items cleared away in one go. Scroll all the way to the bottom, and pull up past the end to clear them away.
If you feel the need to keep them, you could use the batch drag & drop + dragging between lists to move out the important stuff into a new list that will perform appropriately speedily.