Used GPL Library in Commercial Product — Am I Required to Open Source Everything?

I publish illustrative scenarios prepared by my practice. All participants and conversations are fictional. The fictional posts are not posts by real users, accounts of client experiences, or reports of actual results.
Illustrative scenario prepared by my practice.
For informational purposes only. This is not legal advice.
Hypothetical question

Looking for advice on this situation. Used GPL Library in Commercial Product - Am I Required to Open Source Everything? Anyone been in this spot?

Details: I'm in a situation where I need to understand my legal options. Has anyone dealt with something similar?

Illustrative response

Before sending any cease and desist, make sure you actually own the IP you're claiming. I've seen cases where the person sending the C&D didn't have standing because they never properly registered the copyright.