memory problem new macbook air 13" 16GB/512GB

Brand new macbook air 13" 16GB/512GB out of the box, and suddenly there is a memory warning message popping up urging me to quit apps. I've never seen this on a mac before, and I have more than 25 years of experience of using apple products.

I had to ditch my old macbook 11" (8GB/256GB/i7) because of Apple's policy of planned obsolescence (safari and brave more and more useless without any updated certificates for high sierra, the last osx that this machine can upgrade to), but never did I see a message like this pop up. The new one is certainly much faster, but this is not what I expected. Is this a glitch in sequoia 15.1, or can't the macbook access the sdd-disk when it needs extra working memory?

(I did quit Mail which has behaved erratically)