Manager effectively threatened us - What to do?

Sorry to hear about this (insinuating that missing the project will lead to PIP/firing is crass to say the least), but I just want to say that everyone's really stressed out right now and the amount of empathy in the workplace (and beyond) is at a low.

Unless your manager has been consistently terrible to you in the past, I imagine she's just frustrated something is behind deadline and probably perceives you two as needing hand-holding. It's important to have empathy in these situations.

Tactically speaking, getting blocked on code reviews is incredibly common. There's many things you can do here:

1. Be a bit annoying - Ping the blocking reviewers and remind them to do the review. Make sure to follow the advice from the question asking course to make your requests graceful. I particularly recommend the lesson on explaining the impact: Explain The Impact
2. Escalate - If they still aren't reviewing, rope in whoever their manager is to apply pressure. Maybe your manager will give you the power to self-merge as it's an emergency. The important thing is to bring visibility and urgency to the issue. It's easy for stuff like this to get lost in the fold.
3. Make your commits easier to review - This one is great as it's entirely under your control. Your goal as an engineer is to make your pull requests so high quality that your teammates can approve them with high-confidence while barely looking at it. Follow the advice from the code quality course starting from here: https://www.jointaro.com/course/level-up-your-code-quality-as-a-software-engineer/one-diff-one-thesis/

Should I consider switching to a different org, or is it time to leave the company?

If this is a repeated pattern from your manager, you should definitely consider switching, either to a different team or a different company. Given how rough the market is (especially for junior engineers like yourself), I would try a team switch first. Oracle is a good company, and the stock has done well over the past couple years.

I think your manager is getting pressured to PIP their reports and this project is being used to make a decision.

There's nothing much you can do about whoever's making the call to PIP, but Alex's advice covers what you can do to control your impact on the project.