what do symbols next to the chapter names in the journal mean

[Lechungus]

i have green flags in every chapter except the core and farewell (i havent done farewell yet)
because i have a golden flag in core but ive seen other people have stars in every chapter how do i do that

[lieutenantkirtar]

After some searching it looks like a green flag is for completing the chapter, getting the gold flag requires you to clear the chapter and collect everything (berries, heart, cassette) in one play session.

[Perseus]

Exactly what lieutenantkirtar said. Also, stars are just the old version of gold flags.

[_RetroXd]

The green flags mean that you have completed the chapter and the gold ones means that you've completed the chapter with all berries, cassette and crystal hearth.