Hi @Mirco Fragomena , Is there a reason you have your Color Management policies set to Off? In that case your document would have no RGB profile embedded, and the appearance of RGB colors in a document with no profile would randomly change in the future depending on the application’s current Color Settings setup.
Also Hex is an RGB color notation and InDesign allows you to mix CMYK, Lab, and RGB define colors within the document. I assume you are looking for a web/HTML appearance, so set your document’s RGB profile to sRGB, and when you pick the color make sure its mode is RGB not CMYK or Lab. Picking from the Color picker make sure your cursor is in an R, G, or B field and Add RGB Swatch shows:
Or from the Color panel make sure the mode is RGB: