Play "local files" from PC on my mobile device

[Cr0issant]

Plan

Premium

Country

Germany

Device

OnePlus 7 Pro

Operating System

Android 10 / Oxygen OS 10.0.3

My Question or Issue

Whenever I put local songs in a playlist on my PC and download the playlist on my Phone, I can't play them on my mobile device like it used to work just a few months ago.

The songs show as downloaded (shown by the green Icon in the bottom left) but they are greyed out and whenever I press play on one of them nothing happens.

An example screenshot of a playlist with some offline songs is provided.

I already tried the solutions provided by this post ( https://community.spotify.com/t5/Android/Play-quot-local-files-quot-on-my-mobile-device/td-p/80481 ), none of them worked for me.