Thank you but that just gave a shortcut to the browser opening the page.
I have found the solution in the meantime though; within the app info of each app you can set how the app should respond to standard links. The settings switch for this function was already enabled on all the apps, but no links were visible below them. Using the ‘add link’ button however I could manually select the supported links and add them. Afterwards in app linking worked fine.
I suspect this to be a bug since it occurs with every app even though the settings are fine. I’ve now manually added all the links for all the apps that wouldn’t open links and its perfectly working again.