Is there any way to circumvent this? My music player does not currently recognise the tag mp3tag stores WWW as, is there any way that I can stop it from saving as "user defined URL link" and instead save as "WWW" like it is specified in the tag panel.
With a program like mp3diags you can check which tag MP3tag uses to store data.
WWW is saved as WXXX (as you can also see in https://docs.mp3tag.de/mapping) which is according to standard.
A user defined field would start with TXXX.
So to circumvent the problem, the only way I can think of: use a different player.