Some soundtracks from a mobile game, Blue Archive.

Instructions:
Extract the folder to assets > mod_overrides, just like what you do to other custom menu OST.

Soundtracks included:

Constant Moderato
https://www.youtube.com/watch?v=p7ZRQ0BxtMM

Luminous Memory
https://www.youtube.com/watch?v=eM01nJ_lbEo

Lovely Picnic
https://www.youtube.com/watch?v=pRdhcgmbUag

Connected Sky
https://www.youtube.com/watch?v=7c8p0pRxZHM

Step by Step
https://www.youtube.com/watch?v=-8RciEs-ze8

Irasshaimase
https://www.youtube.com/watch?v=8CCLQHzywio

Credit: Lloyd Dunamis (https://www.youtube.com/c/LloydDunamis) for providing the files.

For other Blue Archive menu soundtracks, please check this mod by Izanagi: https://modworkshop.net/mod/33940