Differences between installed and portable HWInfo64

The executable file is exactly same in both editions. The only difference is that the installer edition does install the file(s) into the destination folder (depending on whether it's a 32- or 64-bit system) while the portable one are just bare HWiNFO32 and HWiNFO64 executables.
So that means no additional functions in the installed version vs the portable one.
I remember seeing a thread here and the OP "screenshot"ed like a system summary somewhere. I'm curious how to access that in portable version.
Absolutely same. If you're running HWiNFO in Sensor-only mode you need to deactivate that option to show the main window or summary.