Reproduction steps:

• Equip elytra and obtain several fireworks
• Look directly upwards
• Take off and use fireworks to boost straight up

Effect:

• Particles spawn and repeatedly flash on screen

Expected:

• No photo-sensitivity issues are present in the game

Note: Turning particles to minimal removes the offending particles, but that is arguably a workaround rather than a proper option.

Example: https://clips.twitch.tv/TameLovelyHorseNomNom-yZTMoeeoQys3jaOG