the savegames are saved on the drive where my os (C/:) is located

but i installed the game on a seperate ssd (D/:)

how do i change savegame location so that the savegames are on the same drive where i installed the game

Not sure why you would want to do that.
But there is the possibility to create symlinks.
mklink /J C:\folder D:\target\folder
And yes, this is entered in a terminal

because i want my savegames where my games are ?

i want to keep my os drive clean

i dont see why anyone would want their game and savegames fractured on 2 diffrent drives

I haven't tried but AFAIK, savegames go to :
%homepath%\AppData\Local\Larian Studios\Baldur's Gate 3\PlayerProfiles\Public\Savegames\Story

If you create a .bat file were you set homepath to another location right before launching the game, then savegames would go were you decided (but still under AppData\Local\Larian Studios\Baldur's Gate 3\PlayerProfiles\Public\Savegames\Story).

You would have to start the game from that .bat file instead of the game icon.

Because sometimes I will reimage my C: (OS) drive with Macrium Reflect and if I have saved games on it all my game saves will disappear. My entire windows has admin rights. I run windows in admin all the time. So there this isn't a problem for me.