On Windows:
Create the file
D:\temp\rc_lclwc\lazarus.cfg
In it put the single line
--primary-config-path=D:\temp\rc_lclwc\configs
Then you do not need it on the command-line.
Did you copy your old config?
Some config files contain full path.
And if you copied, then it will warn you that the file was last used from .....
If you start with an empty config folder, the IDE creates all config for you.
You can copy the file EditorOptions.xml. Other files, you need to check for full paths first.
If you got a new config, Lazarus will ask where fpc and gdb are. (it may find your primary install, and suggest them)
You can also start
lazarus.exe --setup
(and --pcp unless you have the lazarus.cfg)
It is ok, to point your 2ndary Lazarus to use Fpc and gdb from your primary install.
Gdb you can just copy to your 2ndary install.
If you copy/move fpc, you need to find the file fpc.cfg and edit it. It contains absolute path to some of the files/folders.