Hi Jenn! I submitted an R&R eight months ago, got proof of receipt and haven’t heard back. Should I nudge? What are the odds of the agent not having gotten around to my manuscript at all? Would they feel rushed to read it at this point and just reject?

I think you should nudge. (Gently!) I feel like the odds are high that they haven't gotten around to it? Because if they HAD gotten around to it, they would have responded. It's also possible they dipped in, got called away, thought "I'll get back to this soon" and didn't get back to it. It's also possible they read it, thought "I'll take some time and formulate my thoughts" and haven't finished…