Improve iPad music

Intro

During the summer I am away more, often without access to wifi or internet.
It is convenient and enjoyable to listen to local music on iPad using the Apple Music app.
However it is inconvenient to update my iPad music by connecting to my PC and using iTunes to add/remove music.
The consequence is that my iPad music is often outdated; it contains albums I don't really listen to and doesn't include current favourites.

Ideas

Apple Music
Apple Photos works well with iCloud, allowing you to look at shared pictures on a range of devices.  I hoped Apple Music might provide similar functionality but it will only sync music if you have an Apple Music subscription (£11 pcm).

iCloud
iCloud looked like it could be part of the solution.  Files can be moved to and from iCloud using iCloud Drive on Windows, Apple Files on iPad or a browser to access iCloud.com.  Free storage is limited to 5GB but 50GB can be added for £1 pcm.
When  you access an iCloud folder your view is synced so all users see the same set of files.  Unfortunately this feature does not include the capability to physically synchronise copies of file onto the local device.  You still need an internet connection to access the files.

Files
Apple Files can access music on the local drive, iCloud or a network share.
Double-clicking on a music file causes it to play within the Files app.
This is interesting but not a practical solution, unless playlists can also be started within Files (I didn't investigate).

VLC
VLC is able to play music directly from iCloud but it would still require an internet connection.

Doppler

A reddit post I saw mentioned that a music player app called Doppler may help with my requirement.  After trying out its features I invested £9 in purchasing it.

Like many music player apps Doppler has a music library.  You can import music to this library from a variety of sources.  I particularly liked the help text Doppler provided explaining various download methods.  Music can be imported from, for example:

1)    local hard drive
2)    iCloud
3)    network share
4)    Apple Music storage

This functionality provides a solution to my requirements.
I started off by importing all the albums from my Apple Music
I then select any new albums I want from my PIP Music database.
As albums are easy to download I can remove ones I don't listen to much and re-add them later if my mood / tastes change.
Once albums are imported I can listen to them without wifi or internet access.
I don't need to use iTunes or even iCloud to make this work

The screen shot below shows the Apple files app which is accessing the pipmusic folders on my PIP NAS.  I can select an album the "share" it with Doppler to add it in.

As I can access PIP if my iPad is connected to  wireguardVPN, I dont even need to be at home to add music to the iPad.