gonna drop some sources I have saved on Pinterest! I don't know if these all link back to the original sources so apologies for that
This one's more for palette building but I think it's useful and can be applied to the other ones
"Chromatic fringe" - I also see people using this with shading, they bring in a transition color that is a different hue than the base color or shadow, it makes it so that less vibrancy is lost and it doesn't get muddy!
Also one of my favorite artists who makes bright and colorful art like this is Not Sorry Art on TikTok & YouTube, her website is here and it's<3 my fav. She has some videos where you can see her process
With the oranges painting you put as an example, I noticed they painted the lighter values more toward yellow - they also exaggerated the hues of the undertones of the photo, so I'm guessing they either did it in their head or bumped the saturation up to get a closer look! I really love these paintings you shared and I definitely share your desire to paint/draw like that :)