Amstrad, there are many factors to consider here:

1. Responsive web design means “the fold” is likely to be in a different place for everyone depending on their screen size and orientation. So part of the problem is that clients don’t fully understand the requirements and implications of a truly responsive design. What fits “above the fold” on desktop is never going to fit on mobile, so we need to be clear that “the fold” really means “the folds” and that plural folds can sometimes be a huge number of potential variations.
2. The initial viewport, before any scrolling occurs, still has value. It’s still a great idea to put your primary message and call to action “above the fold”. What’s changed dramatically is what else is expected above the fold — and the answer is, nothing else! These days it’s normal and expected that the area above the fold is relatively simple, visual, and very focused on that core message and CTA. Contrast this to what used to be done, which was trying to put nearly everything above the fold, and there’s a huge different in expectations about how this area should be used on a modern website.
3. Website with different purposes can have wildly different interpretations for what will perform best above or below the fold. A portfolio site vs. an ecommerce site vs. an app landing page, etc…all have very different needs for what messages and actions should be included there. So knowing the context of your project and its user’s requirements carries far more weight that where the fold is, and outdated definitions of what should be include above it.
4. So it’s not so much that thinking about and defining where the fold is on different devices, and considering what content fits above or below that threshold is no longer important. That will always be relevant. What’s changed is the strategy for what should be included in that area. And when I have clients who are still clinging to a 10 year old strategy for what to include above the fold, that’s when you need to challenge them.