"The project uses target OS=Win64 and CPU=i386. T
Should be CPU x86_64
Usually when you make changes in the "target" settings, you will need a cross compiler.
If (I assume) your setup normally (without an extra settings) generated a 32bit exe, then you have a 32 bit compiler.
(use the windows task manager, it will append "(32)" to any running 32 bit process)
I do not know where and what installer you downloaded, and if that includes a cross compiler or not.
On our SourceForge site there are "Windows 32" and "Window 64" sections. Each have all the versions of Lazarus. Those installers also include fpc for the same bitness.
In addition for each version, there are cross compilers which can be installed into the same directory as you main install.
(The installer also features a 2ndary independent install).
Note: that you also need gdb for the correct bitness (comes with the install or cross-install). And there may be generally issues trying to debug 64bit, if your IDE is 32bit.