My guess was correct, Cyrene eded up becoming a True Damage enabler.

For a resume of her gameplay, check the rest of the post.

Keeping Up With Star Rail — "Cyrene: A Blank Verse for the Future" | Honkai: Star RailYouTube

In summary of her gameplay:

• Basic Attack: Deals damage to one enemy.

• Enhanced Basic Attack: Deals damage to all enemies, dealing more to a designated one.

• Basic Skill: Creates a field that enables every teammate to deal true damage. Last for a set number of turns.

• Ultimate: Non energy reliant, after gaining 24 stacks, becoming memmosprite Cyrene. Using the ultimate for the first time in the battle instantly charges all allies ultimates, even non energy reliant ones, and also dispels any debuffs applied to them. Cyrene gains stacks of charge every time an ally takes action, any kind of action seems to suffice, she can also gain one stack via basic attack, two via basic skill, and three via enhanced basic attack. In her memmosprite form, Cyrene also gains an enhanced basic attack, and her skill zone turns permanent.

• Ultimate skill: Once Cyrene gains 12 stacks after using her ultimate, she can use an Ultimate Skill that divides into two possible actions.

• Ultimate Skill, Buff: Buffs the damage of a designated ally from the team. If the ally is a Chrysos Heir, they gain a specific buff depending on which one they are.

• Ultimate Skill, Attack: Deals damage to all enemies.

• Technique: Creates a field around the character that improves Cyrene's mobility and frozes all enemies withing range (not the same as Jingliu's freeze), once entering battle, the basic skill is instantly casted. The field remains active even if Cyrene is off field.

The specific buffs give to each Chrysos Heir are the following:

• Aglaea: her talent stacks reach maximum immediately, she also gains a special buff that makes her regenerate energy each time she or garmentmaker attack, this energy recharging buff lasts for a certain number of attacks. She also gains a DEF ingoring buffs that last until her Ultimate Enhnanced state ends.

• Tribios: Her damage gains a DEF ignoring buff and her follow up attack deals more damage if her Ultimate is active.

• Mydeimos: Cleanses all debuffs on him, if Mydei is already on his enhanced state, immediately launces his follow up attack without consuming the charge and with enhanced Crit Damage, if Mydei is not on his enhanced state, he takes action immediately.

• Castorice: Castorice's Ultimate charge can charge up to %200, when using her Ultimate with %100< charge grants a DMG multiplier equal to the % above 100. The DMG multiplier scales a bit the less enemies are on the field. The %100< charge does not remain charged after Ultimate, it's completely consumed for the buff.

• Anaxagoras: Recovers 1 skill point, Anaxa's skill deals an additional stance of damage, after using basic atk or skill, Anaxa grants an ATK and skill buff for all Erudition units until Anaxa's next turn.

• Hyacinthia: Recharges energy, gains a healing buff that only last for a limited amount of uses.

• Cifera: Buffs her damage and DEF reduction, she can also reduce the DEF of adjacent targets to her skill.

• Khaslana: Gains 6 coreflames, when using coreflame, increases Crit DMG for every excess coreflame charged, and also gains a crit rate boost. Once his Ultimate ends, Khaslana does not go back to default but her Ultimate form is stretched until he runs out of HP. During these stretched turns, Khaslana gains scourge for his first additional turn and his attacks deal more damage, but each attack consumes a set amount of HP percentage.

• Helektra: Gains a Energy recharge buff that regenerates Energy by each attack, like Aglaea's, this buffs has a limit of usage. Increases Helektra's damage, and each of her attack causes the DoT to be pre-triggered causing a set percentage of the original damage.

• Cerydra: Increases the ally selected by Cerdra's skill's Crit DMG. After her duplicate skill ends, the stacks go back to 1 instead of 0.

• Evernight: Increases her memmosprite enhanced skill damage, and also boosts her Crit DMG buff.

• Dan Heng Permansor Terrae: Buff Souldragon and his shield granting effect. when casted, advances Souldragon to take action, deal an attack isntance without consuming charge the first time.

• Remembrance Trailblazer: Increases his ATK and Crit Rate based on her HP and Crit Rate. After Trailblazer uses his enhanced basic attack (Trailblazer will gain a enhanced basic attack after completing the 3.7 story) Cyrene throws an additional Ultimate Skill, Attack.

• Cyrene: Each time Cyrene uses Ultimate Skill, Buff on a Chrysos Heir teammate, she gains 1 stack, once the stacks reach 3, she immediately launches an Ultimate Skill, Attack and gains an extra turn.

On an additional note, seemingly Cyrene is an HP scaler.

In the end, Aglaea and Trailblazer ended up being the exceptions for the Remembrance main scaling.

In short, her gameplay consist on using a formation that includes Chrysos heirs and take advantage of their buffs.

Once you collect the 24 stacks for her ultimate, she transforms into memmosprite Cyrene (whose name was censored on the description, so maybe lore implications soon), and once then, Cyrene's Ultimate turns to need 12 stacks, and she can only uses enhanced basic attack, her skill remains active, and her gameplay consist on charging her skill to use it on as many allies as possible and as much times as possible.