Travel TO Switzerland is 100% legal. When coming back from Switzerland, you have to enter into a mandatory 10 day quarantine; if you test negative after 5 days, the quarantine stops. However if you can prove that you have only been in Austria and Switzerland in the 10 days before entry in Austria, there is no quarantine or test requirement. Currently Switzerland demands travellers that have stayed in Land Kärnten, Land Salzburg, Land Steiermark or Land Upper Austria to go into a 10 days quarantine upon arrival in Switzerland. Please check this page for the latest list of Austrian regions affected by this Swiss regulation.
Info found on this page on Dec. 7, 2020. Please consult the disclaimer