I need to know everything about Dex?

I am not sure what I am looking for but trying to do some research on how Dex effect game play on certain builds.

Has anyone noticed anything significant involving Dex?

DEX is used to stabilize the difference between the maximum and minimum damage you do, and the maximum and minimum damage you take from enemy attacks.

However, in regards to your own damage, DEX becomes mostly insignificant when you are using 7☆+ weapons; this is because 7☆+ weapons have a bonus to them that raises your minimum damage to ~90% of your maximum, which is in general higher than you can normally get through raising your DEX with Skills and Augments.

When it comes to the damage you take from enemies, you usually get better damage mitigation from raising your HP and Def, at least in regards to the effort of raising your DEX significantly outside of what you can naturally get from leveling and Title Bonuses.

In general, the only builds where DEX is significant are Braver, Bouncer, and Phantom based ones just because they have Mag Skills that directly convert any DEX on your Mag into Pwr (MEL and RNG for Braver, MEL and TEC for Bouncer, and MEL, RNG, and TEC for Phantom); this is particularly significant for Br/Ph and Bo/Ph since those Mag Skills will stack with each other.

Other than that, DEX's biggest significance currently is for equipping certain high-rarity weapons and units. For these, your best option to get DEX is to level Braver and Bouncer to lv75 to be able to get an extra 60 DEX from their Title Bonuses (30 from Br, and 30 from Bo) added to your base stats (ie. the ones used for equipping).

Guess I have to do an in-depth quest on Dex myself.

Starting with maxing out Dex on my Braver sub.

That's quite literally the gist of what DEX does... It's useless outside of mags for braver, bouncer, and phantom.