If anyone is still having issues with StudioLink, please follow the below instructions:
If you're unable to access StudioLink in Affinity Publisher, make sure you have installed the 1.7.1 updates (as described here) for both Affinity Photo and Affinity Designer. After you have installed the 1.7.1 updates you will also need to run the apps at least once before reopening Affinity Publisher to access the StudioLink feature. If StudioLink still doesn't work, please try the following:
If you're using Windows go to %ProgramData%\Affinity\Common\1.0\appinfo\Release and rename the Photo Release.appinfo and Designer Release.appinfo files. (as Photo Release OLD.appinfo and Designer Release OLD.appinfo respectively) Once renamed, re-run both Designer and Photo and try StudioLink again. NOTE: If this works for you PLEASE can you upload those renamed files to us to investigate further.
If you're using macOS, make sure that all Affinity apps ( Publisher, Photo & Designer ) are in the root of the Applications folder.
Please create a new thread if you can't link the apps after trying the above, so we can investigate this further, many thanks!