Hi!
I would like to thank you for the APT repository.APT has been transitioning to a "new" format for the files in /etc/apt/sources.list.d.

The new version, zettlr.sources (instead of .list) could have the following content:

Types: deb
URIs: https://apt.zettlr.com/
Suites: ./
Components: 
Signed-By: /etc/apt/trusted.gpg.d/zettlr_apt.gpg

(this was obtained by translating the zettlr.list file to the new format using apt modernize-sources.

By the way, there is a tool in the Debian
repositories, called extrepo which allows to manage
external repositories like yours. It would be great if
the information about zettlr could be added there:

This is the repo where information could be added:

https://salsa.debian.org/extrepo-team/extrepo-data

Cheers