The shirt in the image is indeed from the brandMarks & Spencer (M&S).
It is specifically identified as anM&S Sartorial Regular Fit Shirt, likely a luxury pure cotton textured shirt or a cotton-linen blend shirt in a light blue or sky blue color.
Product Details
Brand:Marks & Spencer (M&S)
Collection:M&S Sartorial: a luxury tailoring range inspired by Savile Row craftsmanship
Color:Light Blue / Sky Blue
Fit:Regular Fit
Material:Often 100% pure cotton, sometimes a cotton-linen blend, with a subtle textured weave
Features:Typically includes a classic collar with removable collar stays, adjustable cuffs, and an easy-iron finish for convenience