@whitequark it looks as if in my "advanced DNS" (namecheap), the actual domain is *not* allowed to be in the "host" column, so for me that says just _git-pages-repository.sub1.
now dig _git-pages-repository.sub1.swiss-soccer.net TXT includes an ANSWER section with
_git-pages-repository.sub1.swiss-soccer.net. 1799 IN TXT "https://codeberg.org/nxskok/sub1.git"
which is a lot more encouraging.