Linking my Trinity build thread again: https://dormi.zone/post/3820647
Trinity is in a weird place. She was the OG sub-tank and support, but I see her role shifting more over time to three areas: low level challenge content (especially sorties), gun buffs, and shield management.
I kind of wish she could use Vampire Leech to put shields on defense objectives. I still feel slightly delirious that it's Mag and Mag alone who can Overshield Mirror Defense objects...
Trinity was an early favourite frame when I was new to the game, as for new players she provides very easy energy economy, object defense, excellent survivability, and status immunity. She's lapsed a bit in that role, being now stuck behind one of the two token-walled Assassinations currently in the game, and all the way in Pluto, close to the end of the Star Chart.
As an older frame, Trinity also has excellent Helminth flexibility for a variety of roles and mission types. The aforementioned traits also give you a lot of leeway to try fairly extreme builds, or alternatively a safety net to splash out into new playstyles.
Trinity's unique support contribution is shield management, although with Dante essentially godmoding the squad as long as each player can continue to get assists, this is a lot less valuable nowadays. In the build thread I linked, I abuse this to keep Empowered Blades rolling for truly excessive AoE nuking through Melee Influence. 75% DR is nothing to sneeze at either, being equivalent to placing an Eclipse on the whole party. This bumps shields to a respectable 87.5% DR, enough for non-scaling content, even EDA. This can also extend the effectiveness of other frames' shield support, such as Hildryn's Haven and Protea's shield grenades.
Finally, as a tl;dr on that thread I linked, Trinity is quite surprisingly equipped as a murder machine. The rework improving her animation lock syndrome, and the buff to the base number of Links means she is very fast and fluid, and has a very high KPM potential (with Abating Link). Energy Vampire being a built in energy management tool means she can run aggressively high power strength builds very comfortably.
"Trinity is a DPS frame" makes me feel like I'm in a fever dream though. I don't know if I'll ever get used to that.