I have set up Fedora KDE 42. I have added in the winehq repository, as described on the page Fedora · Wiki · wine / wine · GitLab.
The URL of that repository specifically mentions version 42 of Fedora.
My question is what happens when the system is upgraded to Fedora 43? Is there a way to have the third party repository URL automatically change to 43 as well?
Not without something altering the URL to point to the 43 version of the repo. That may be you, or it may be a script which someone provides but I’m fairly sure it won’t be automatic.
There’s a special variable to handle this:
dnf5.conf: DNF5 Configuration Reference | Man Page | File Formats | dnf5 | ManKier
But their repo is not ready for F43 yet:
https://dl.winehq.org/wine-builds/fedora/43/