Is there some kind of practice mute for flute? I have been lent a flute and would like to try it out without disturbing neighbours too much. Only found for trombones and such when googling.
Assuming you are talking about the standard orchestra flute, or another kind of traverse flute: no, it's impossible to mute a flute.
Brass instruments such as trumpet or trombone can be muted because all of the sound comes out of the bell. The sound of a flute is far more diffuse.
For other members of the flute family, fipple flutes, there are mutes available. Here's one for recorder (note the site says "flute" but they mean "recorder").