Like the short description says.
Credits:

Top screen:

Sora: From Kh3 Secret ending
Aqua: From https://www.ps4wallpapers.com/kh3-aqua/ Uploaded by Zenithium.
Roxas: From in game taken from https://www.khwiki.com/Roxas
Axel: From https://www.pinterest.co.uk/pin/363525001168508630/
Soras Background From: https://www.kh13.com/news/updated-kingdom-hearts-iii-data-mining-project-reveals-interesting-in-game-assets-including-features-from-scala-ad-caelum-daybreak-town-verum-rex-and-more-r3118/
Roxas Background: https://www.zerochan.net/625467

Bottom Screen:

Ventus: https://www.hiclipart.com/free-transparent-background-png-clipart-xvbqp by UXIAN I know this was in game stuff but this person made the background transparent.
Riku: Kingdom Hearts 3 Secret ending.
Lingeringwill/Terra: https://www.zerochan.net/1873033
Xion: In game asset made transparent by https://kingdomhearts.fandom.com/wiki/Xion
Ventus background: https://www.pinterest.co.uk/pin/734297914226133677/ uploaded by Arthur.
Riku background: I cant find the source to it I even backtracked with the original title I will have to look into it.
Lingering Will / Terra background: https://www.kh13.com/news/new-original-world-scala-ad-caelum-revealed-in-kingdom-hearts-iii-final-battle-trailer-r2767/
Xion Background: https://gamewith.net/kingdomhearts3/article/show/15019

Folder Icon:
Cloudy background: https://www.shutterstock.com/search/pink+clouds uploaded by ChunnapaStudio
Crown Icon: https://www.nicepng.com/ourpic/u2q8w7y3o0r5r5y3_kingdom-hearts-crown-png-clipart-library-stock-kingdom/

Icon:
Heartless Clipart: https://kingdomhearts.fandom.com/wiki/Shadow

Kingdom Hearts 1.5 HD ReMIX OST - Always On My Mind