It never starts dramatically. There is a bag of things from your mum's house that you will go through later. A slow cooker that was a bargain and might come in useful. A bike that someone was definitely going to start using again. Then one morning you cannot get past the hallway without turning sideways, and nobody is quite willing to admit how it got to this point.
Clutter has a way of accumulating quietly, then all at once. The good news is you do not have to overhaul your entire house on a Saturday afternoon or make any difficult decisions about what stays and what goes. You just have to get it out of the way for now.