I want to install WM but feel as in KDE Plasma, but nore lightweight, can you advice that?
You aren’t going to find another environment that is similar to KDE but lightweight.
Either switch to a WM and accept that it will be different or make changes to plasma to make it more lightweight.
Probably LXQt would be the closest (I know it’s a DE, not a WM) it is QT based and it’s pretty light.
Perhaps if you describe what you want to achieve with a window manager, some one of us who live and breathe wms might be able to help. As Dalto noted if you want to do what KDE does, the best way to achieve that is by using KDE. If you want to do something different, lighter (whatever that might mean) you will need to describe what that might be. Once we know what you want to do we might be able to point you in a useful direction. In the short-term I recommend you read up on wms (dozens of them) on the arch wiki to get a rough idea of what is ‘out there’.