Gig Performer is a 64-bit application and so can only load plugins that are also 64-bit.
However, there are some applications available that can wrap 32-bit plugins so that they can be loaded by 64-bit hosts like Gig Performer. Click here to learn more: https://gigperformer.com/how-to-load-32-bit-plugins-with-gig-performer-on-a-mac/