Identify orange-brown, teardrop-shaped insect in central Europe that was found indoors
I think it may have been a tick of some kind, one that had already fed and was round (hungry ticks are sort of flat).  I couldn't say exactly what species.
I'm not sure, but that's the only thing I can think of that matches this photo.  I'm no professional, so another person here may be able to do better.
Ticks have eight legs (they're vaguely related to mites, and, even more distantly, to spiders), so I was puzzled at first by you saying it had six legs, but possibly what you thought were its antennae were its other pair of legs?  (Ticks have no antennae).
https://en.wikipedia.org/wiki/Tick