with specifically the highlights and colors being hues that compliment each other, don’t distract from the scene, and make it more interesting/visually appealing

cohesive but still contrasting

This kind of talks about color and composition

This is a bit about landscape specifically

Values & composition

Contrast in composition

Balance in colors & values

This one's more for palette building but I think it's useful and can be applied to the other ones

Cohesion within compositions/lighting

"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!

This one specifically has a lot of process behind the style of painting you're looking for!

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