The Ryzen 7000 series IGP is known as Radeon Graphics 128SP. It is based on RDNA 2 architecture, has 2 compute units and as the name implies, 128 shading units.
https://www.techpowerup.com/gpu-specs/radeon-graphics-128sp.c3993
The GTX 660 has way more cores and shaders, however most cards are limited to DirectX 11 and don't support DirectX 12 games. Plus drivers for Windows 10/11 may not exist.
https://www.techpowerup.com/gpu-specs/geforce-gtx-660.c895
If you're playing older games the GTX easily outperforms the IGP, however if you want to play modern DirectX titles you'll have to use the IGP.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT
Ryzen R7 5700G | B550 Gaming X | 2x8GB G.Skill 4000 | Radeon Vega 8 IGP
Ryzen R5 5600 | B550 Gaming Edge | 4x8GB G.Skill 3600 | Radeon RX 6800XT