Many things are ping-dependent in this game, from testing we can deduce that certain things are updated client-side while others are updated server-side. The complete list of high ping interactions is documented below. See the Vault Entries for more details.
Client side
Elemental Reactions and Auras
All character stats except for HP (including buffs)
Resistance Shred
Construct HP
Server side
Damage and hits
Character and enemy HP
All enemy stats
Energy particles and character energy
Stamina
Weapon stacks
High Ping Interactions
Elemental Reactions still work, including the Resistance Shred from Superconduct.
Both player and enemy are granted immortality whilst under high ping but the HP bar will be updated once switched back to normal latency.
This can lead to Bennett's Burst ignoring the HP threshold or Albedo's A1 not benefitting from enemies being below 50% HP.
Energy is not produced under high ping but will be generated when ping returns to normal.
AA energy source is not refunded when back to low latency.
Energy is not consumed when under high ping.
When enemy is aggro-ed by player before high latency, it will remain aggressive.
When enemy is aggro-ed during high latency, it will remain passive for the duration of high latency state.
Taunts will turn aggressive enemies to passive enemies under high latency.
Character stat buffs still update normally, unless they are related to other stats that are updated server side, such has Hutao's passive from being below 50% HP.
Resistance shred works.
Fall damage is dealt.
ICD behaves normally aside from a few exceptions, so far only the Rainswords from Xingqiu E have a different application rate than usual.
Healing is inaccessible during high latency. When returned to low latency, the healing will be applied, and healing like Bennett's Q will ignore the HP thresholds.
Character shields work normally under high latency.
Stamina is not consumed under high ping, nor will it regenerate.
For conditional weapon passives (Lion's Roar, Dragon's Bane), if condition is true, the passive will be added into the damage calculation.
On-hit passives (Flute), sacrificial/favonius weapons cannot trigger under high latency, but Aquila Favonia seems to still work.