No need to pair program, you can always send a message to your colleague about the design of the upcoming code, especially if it’s going to impact them or if it’s an area that they’re more familiar with. Waiting till a PR for feedback is wrong IMO.

Code review is not for feedback, it’s for ensuring quality (many eyes on the output) and have a shared involvement in the evolution of the code. The time for feedback is earlier, once you have an idea of the solution.