Assuming you are using a recent version of Lightroom Classic…
You are free to manually sort the files by drag-and-drop, in addition to the provided sort orders (Filename etc.)…specifically when viewing the contents of a single folder. However, if the Library module is set to view the contents of a folder and all its subfolders, then Lightroom Classic won’t allow manual sorting.
Manual sorting is possible, regardless of folder organization, if you create a Collection (a virtual list, like a playlist), and add images to the collection. For example, you would be able to create a collection, add all 48,000 images to it, and be free to arrange with no sort restrictions, because a collection is abstracted away from the file system.
Exporting is a different matter, because when you export the files to a folder on your desktop, computer file systems generally have no way to store a custom sort order. You can use only the sort orders provided by a window on the desktop, such as File Name, Date Created, etc. To preserve sort order outside Lightroom Classic, many of us use the custom file renaming feature in the Export dialog box to add a number sequence token to the beginning of the exported filenames. That numbers file names based on the sort order that was in effect in the Lightroom Classic view from which you exported. For example, if you manually sorted so that “box.jpg” comes before “airplane.jpg” which is alphabetically earlier, you can configure file naming on export so that they become “001-box.jpg” and “002-airplane.jpg”. That will preserve their manual sort in a desktop folder window set to sort by filename.
As for getting all this over to Linux: If you set the Export dialog box in Lightroom Classic to include all metadata, then the metadata you entered in the IPTC panel (such as keywords, captions, etc.) in the Library module will be embedded in each exported image. IPTC is an industry standard read by many photo applications, so the next IPTC-compatible application to read those images would see your metadata annotations.
I am not very familiar with Linux, but I am aware of two free and open source Linux applications that are kind of like Lightroom Classic: Darktable, and Lightzone. You can try them out and see if they do a good job of reading the annotations written by IPTC-compatible applications such as Lightroom Classic.
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