This is a user script (to be used with Greasemonkey, Violentmonkey, and similar packages. It automatically adds a download button for `.bib` citation export to Springer Link publications. Enjoy!

fix_bibliography_links_springer.js

// ==UserScript==
// @name     Fix bibliography links @ Springer
// @author   Pseudomanifold
// @include  https://link.springer.com/*
// @include  https://*.springeropen.com/*
// @include  https://*.nature.com/*
// @require  http://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js
// @version  0.0.2
// ==/UserScript==

/*
  Are you also as baffled by Springer's website as I am? Some publications present
  you with a link to download citations using the .ris format only. I have *never*
  used this format since .bib is vastly superior. Obviously. To add to my confused
  state, some publications actually permit you to download a citation in more than
  the .ris format. What gives? I have absolutely no clue why this is the case, and
  of course Springer does not answer my queries. Hence, this script. It will solve
  this issue and will add a link with the right format. Neat.

  (╯°□°）╯︵ ┻━┻
*/

var BibLinks  = $(".c-bibliographic-information__download-citation > a");

BibLinks.each( function() {var jThis   = $(this);
    var bibLink = jThis.attr('href').replace(/format=refman/, 'format=bibtex');

    jThis.parent().append('<a href=' + bibLink + '>Download citation (.BIB)</a>');
    jThis.parent().append('<svg width="16" height="16" focusable="false" role="img" aria-hidden="true" class="u-icon"><use xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#icon-download"></use></svg>');
	}
);