Rainer,
to quickly find a topic that STARTS with the letters IN, simply click into the topic list and type "in" fast enough - you will be taken instantly to the topic that starts with "in".
If however, you prefer to find any instance of "in" within a topic title, use the GoTo function. Since most programs (Microsoft Word, Excel etc) have Ctrl-G (German STRG-G) assigned to GoTo, I decided to make CT compliant with the rest.
Tools > Options > Keyboard > GoTo, then assign Ctrl G, if this is it what you want.
this would be very useful: I could assign the "in" page to a keyboard stroke.
You cannot assign a keyboard shortcut to a specific topic, but if you need your "in"-page more often, assign a Bookmark to it, or create an outline-entry pointing to it, or put a link on your start page, or even better, make your preferred topic the main topic, then tell CT to always open your project with the main topic. (right-click project-tab > Properties > Tabs General + Options)