FWIW, I’ve never been that satisfied with any sort of “mute” for a wind instrument. Most of my experience is with pennywhistle, but I find I’m less happy with the options for recorder.
Methods I know of:
–fold a piece of paper or card and hang it over the edge of the labium
–put a piece of tape across the window (not completely covering it; you’ll need to experiment with position)
–put a paperclip or similar in the windway (never tried this on recorder, didn’t like it on whistle)
The problem with these is that yes, the instrument will get quieter… but the higher notes won’t sound at all (in which case you might as well just finger the instrument without blowing), and forget working on your tone or higher notes. Easier just to take the instrument outside or some other place where I can play as normal without bothering anyone.
(Yes, I live in an apartment with very thin walls, so I know all about not wanting my neighbors to hear my playing. As I type, I am listening to my upstairs neighbor’s phone conversation; I can nearly make out the words. If he was in the basement or in the hallway, I’d hear him clear as day.)