A fired employee is still eligible for unemployment as long as they were not fired because of specific misconduct. Poor performance does not constitute misconduct. Misconduct must be “willful and wanton.” (Regularly missing work or being late, stealing, fighting with coworkers, etc.)
The CA guidelines are long, but contain some useful examples and guiding principles: https://edd.ca.gov/en/uibdg/Misconduct_MC_5/
I know of people who should have been fired who were talked into quitting instead just because quitting means they can't sue. In turn the company gives the official answer "X worked here between these dates and left in good standing". Since the company always said the same thing when asked if someone worked there it wasn't a negative to the next employer, while if they fired they would have to say left in bad standing.
Of course since getting fired is a sensitive issue I won't say who. Reading between the lines in conversations and how the company acted though I'm sure that is how it worked.
Note that there is a difference between being sued and losing in court. Even if you win you still need to pay your lawyers. I've had one lawyer tell me about spending nearly a million dollars in court for a case that was about $100,000 in asked damages that the lawyer knew based on facts they would lose - but [I can't talk about this part] made it impossible to figure out how to settle out of court.