I read down pretty far and did not see this basic advice: you need a lawyer. Hire a very good one: they are cheaper than poor lawyers by an order of magnitude. That lawyer will review your agreements, the state laws and the communications with the company and tell you where you’re at. You could all go in together for the lawyer btw if you have the same contract. I bet that lawyer will tell you (if this is in Californ…
In the US, I've worked with the team at https://www.optimalcounsel.com/ before. They're great and founder-focused so generally get it and are reasonable on pricing.
Before you talk to an attorney, make sure you have your agreements together. That is likley your initial employment agreement, any grant docs, your separation docs, and the current agreement they want you to sign.
And yes, don't wait. If you need to take action, you may need to have time to ship docs, send wire transfers, etc.