Very interesting post, @gadrian. To answer your question:
'What do you think about food supplements? Do you use them? What for?"
Yes. For improving basic health, as without your health, what are you doing instead? 🤷♂️Just common sense, although ... How "common" it is might be considered a worthy debate, if one just looks around here in America ... 😉
The fundamental question is what you touch on in your post - what is happening to the nutritional content of our food? Definitely on the decline here ... An excellent book on this topic? This one is highly recommended - "Good Energy"
With our recent election results, this topic (of your post) will be hotly debated here in America for some time to come. "Elections have consequences!" Yep. We'll see how it goes.