Google Play Music is LONG gone - replaced by YouTube Music. Users were urged to migrate their Play Music libraries to YouTube Music... which we should all have done by now. However, in opening YouTube Music you should have the option of uploading your library.
Use a file explorer to COPY the files into your library prior to upload. I like Solid Explorer because it has two navigation panes in landscape mode: I can go to the source folder on one side and the destination folder on the other, then copy it. I rarely ever MOVE files - especially multiple files - because an error during the move could corrupt them. Once I know they're safely copied, I can delete the old ones.
