All trains that are used with the pass require a valid activated day and entry on pass, this includes S-Bahn.

There are some side benefits including some tourist lines where a pass will allow a discount on purchased tickets, these do not require an active travel day. These are listed on app under More tab and on interrail website.

IF you stay there and only use it for some short local trips, then do not waste a passday on it (unless it is continue anyway)-a local dayticket for ALL bustrammetro/+Sbahn will be cheaper-even still in the Swiss

S-bahn exist in nearly all major German and Austrian towns and also Copenhagen. Many more cities are catching on to this brand.