Q: Connect iMac G5, 2005 to TV via usb to use tv as monitor

Not what you want to hear but I'd suggest posting in the Power PC forum. This forum is for Intel based iMacs.

one does not really connect displays using usb

most usb ports in tv's support usb mass storage usb driver only

read more

https://en.wikipedia.org/wiki/USB_mass_storage_device_class

and no computers see a connected usb device as a display without special software running on the computer

In 2005 the "DVI to Video adapter" was the way to connect an older pre-HDMI TV.

In 2006 the "Mini DVI to Video adapter" was the way to connect an older per-HDMI TV.

see > About Apple video adapters and cables - Apple Support

I used to do the "Apple Mini DVI to Video adapter > S-Video cable > to older TV" setup. It worked fine for years.

Apple DVI to Video adapter.

The TV output end of the adapter has both a Video and S-Video output.

You will very likely need to buy one on-line, because the Apple Stores and most of Apple's other resellers no longer carry those old adapters.