The error message seen over the audio player on start is fixed; had some friends test it on iPhone and iPad iOS 14.1, but we don't have an old iPad. The player was tested and the embedded version, in our remodelled Xara template, has been tested too. Please note that in the demo, in Chrome / Edge, cross-origin prevents the OP's tracks playing.
https://initiostar.co.uk/demo/jp/

Click image for larger version.  Name: iPhone11.jpg  Views: 50  Size: 134.8 KB  ID: 129236 Click image for larger version.  Name: iPad iOS14.jpg  Views: 61  Size: 64.9 KB  ID: 129237

BRIEF EXPLANATION

1. It has been an interesting exercise and challenge to accommodate the way different browsers manage the audio tag with on-start autoplay; one solution, without lots of code, is to create a short (in this case silent audio) track that provides the player with a valid source. You could use a short audio introduction to the playlist too.

2. The image of the embedded player in older iPads distorting to the right in the OP's example is possibly (or not) related to a conflict with Xara's Scale-to-fit-Width being in use for the stand-alone player. In the updated demo, the iframe tag is styled and wrapped between <div> tags to maintain the aspect ratio of the embedded site. It may (or not) resolve the older iPad rendering issue. It might be that setting the placeholder H & W to fixed dimensions would work too (but haven't tried).

The whole exercise of trying to build a simple player (which only started with this thread) has been one of seeing what could be achieved without dozens of lines of code, or the adoption of a 3rd party player. The OP's original player will not work on iOS14, really only two choices - get another 3rd party player that does, or have a go at making one.

If anyone has an old iPad and can test the site that would help us to conclude this thread.

Gary