Ganyu build recommendations

Freeze Ganyu gives a lot of i-frames since you would be spamming Elemental Burst from all of your party members off cooldown. Ganyu's Elemental Burst can deal a ton of damage based on how grouped the enemies are, due to the quadratic scaling on her Elemental Burst.

Regarding Weapon Choices

Polar Star
This weapon is much harder to optimize with, due to having a very high Crit Rate stat resulting in your Crit Rate going well above 100%. However, if optimised properly (i.e. very little Crit Rate substats), it pulls quite far ahead of all the other options.

Aqua Simulacra

Due to the sheer amount of Crit stats you can get from Blizzard Strayer (4), Ganyu's ascension passive and this weapon itself, you can consider running an ATK% circlet, especially if it has better substats than your Crit DMG one.

Amos' Bow
In quickswap heavy rotations (Ganyu Mona Venti Diona) where you usually don't do a lot of Charged Shots, this weapon performs worse than the other 5 star options listed.

Prototype Crescent
Similar to the Melt Build, this weapon at higher refinement levels and good passive uptime can pull ahead of some of the 5 star options such as Thundering Pulse and Skyward Harp. However, do bear in mind that not all enemies have weak spots that you can headshot, which does affect its performance significantly.

Regarding Artifact Sets

Blizzard Strayer (4)
This set is the go to set for a Frozen team comp due to the huge stats it provides.