When requesting styles there a specific request format. Styles are coded by volunteers and to facilitate (and partially automate) their work it is necessary for you to provide examples using the exact publications they request:

https://github.com/citation-style-language/styles/blob/master/REQUESTING.md

damnation, I checked the link you sent and it's unfortunately that style appears out of date. The rendered output doesn't match the recently published citation style. Nevertheless, it's a good lesson to search the repository by journal name, too.

However, I did end up figuring this out. To the best of my knowledge, the Thieme-German (Deutsch) available on the Zotero style repository (https://www.zotero.org/styles/thieme-german) is the same thing as Thieme-English. In fact, someone from the journal even told me to use Thieme-German.

In case it helps anyone else, the Thieme-German (Deutsch) .csl file found in the Zotero style repository cannot provide abbreviated journal names by default when using Quarto to render your document. That was one reason I was originally interested in asking for a .csl for Thieme-English. I solved the abbreviation issue by downloading the NCBI journal abbreviations JSON file at https://github.com/citation-style-language/abbreviations/blob/master/ncbi/json/ncbi-abbreviations.json. In my YAML file I referenced this JSON file with the citation-abbreviations argument.

Finally, I found that I also needed to manually add some journal names and abbreviations key-value pairs to the JSON file. For example, my .bib file referred to some journal names with an ampersand (&) while the JSON file referred to those same journals using the word "and". For example, Medicine & Science in Sport & Exercise did not initially abbreviate because the JSON file documented this journal name as Medicine and Science in Sport and Exercise. I also had similar issues with the word "The" in the journal name. I manually added lines to the JSON file as needed, and now I get abbreviated journal names as expected.

I guess what I mean is that I recently learned the International Journal of Sports Medicine (IJSM) available in the repository csl is out of date. However, the Thieme-German (Deutsch) csl is up to date and is the current preferred citation style by the ISJM. It also happens that Thieme-English is equivalent to Thieme-German (Deutsch), at least as far as I can tell. Given that, I don't think there's anything that needs fixing. If something is still unclear, please let me know.