Is there any practical benefit to installing my old RTX 2070 Super alongside my new Radeon RX 9060 XT?

For normal gaming, you should expect practically no benefit. Modern games generally cannot combine two unrelated GPUs, and older SLI/CrossFire support was limited even when both cards matched. Running both can increase heat, power use, driver complications, and may reduce available PCIe bandwidth depending on the motherboard layout.

The 2070 Super could still be useful for specific workloads: CUDA applications, some video-editing or rendering software, local AI experiments, or passing the card through to a virtual machine. Those programs need to explicitly support multiple GPUs, though, so it will not automatically accelerate everything.

An extra GPU can also drive additional monitors while the Radeon handles gaming, but most systems can already manage several displays from one card. Make sure the power supply has the required connectors and check how the second slot affects PCIe lane allocation before installing it.

There are a few niche gaming setups where a second GPU handles tools such as frame generation or Lossless Scaling while the main card renders the game. That can work, but it often takes configuration and may not look or perform as well as the game's built-in FSR or DLSS options. It is not a general-purpose way to increase FPS.

The simplest choices are to keep the 2070 Super as a backup, sell it, or use it in another PC or home server. Installing it just because you have an empty slot mostly gives you extra heat and electricity usage. Keep it if you have a specific CUDA, VM, rendering, or multi-monitor workload that needs it.