Passive simple,when used without auxiliary

I am doing B1 French and reading Camus La Peste( hard going sometimes) On page 173 he says"elles suffirent" which I take to mean they were enough,and I struggled with the conjugation but I found it as passive simple on the Lawless website. I interrogated Gemini AI and it suggested that passive simple is a compound tense requiring auxiliary from etre...despite its name. It also suggested Camus often used passe simple in a stylistic for without the auxiliary. So,is the Lawless conjugation right,and is elles suffirent passe simple, and please,what is going on?