HAM Radio Organizations
The HAM Page of the Swiss Federal Office of Communications, BAKOM: https://www.bakom.admin.ch/bakom/de/home/frequenzen-antennen/frequenznutzung-mit-oder-ohne-konzessionen/amateurfunk.html
Union of Swiss Short Wave Amateurs, they manage the local associations and the use of the frequencies for relays and automated stations: https://www.uska.ch/en/
Most likely the best way to prepare for the exam is attending a preparation course from a local Association, of have a brother who did and forwarded all the background info and documents to me. ;) But apart from having a brother I did the following:
The online version of the books I read: https://www.darc.de/der-club/referate/ajw/darc-online-lehrgang/ - again in German. They're mainly geared towards the German exams but the knowledge contained is useful for the Swiss exams, too.
I mainly used the HamRadioTrainer to prepare for the exam. This is a Windows application which however works pretty well in wine. I was told that the Swiss questions are rather old, 2017ish.
I was told that there are mobile apps with more recent questions but I couldn't be bothered to check whether they exist on F-Droid.
The BAKOM also has a site about the exams, containing PDFs with example questions, of course again everything in German: https://www.bakom.admin.ch/bakom/de/home/frequenzen-antennen/funkerpruefungen/amateurfunk-pruefungen.html