ive been noticing the EXACT SAME PROBLEM whenever i would export an image from procreate and it drove me CRAZY that my art would desaturate all the time. anyway, if you're in a canvas, go to settings > canvas > canvas information > color profile
once youre in color profile, if your current color profile is display P3, CHANGE IT!!!!!! it is desaturating your colors. you're gonna want to change it to sRGB IEC6 1966-2.1 instead
if you're starting a new canvas, you can just go to color profile and change it that way. im SO grateful for this post for giving me the push i needed to experiment with procreate files and finally see what was changing my art to be so desaturated
anyway yeah. tldr if youre using procreate, make sure your color profile is sRBG IEC6 1966-2.1