I often used the word 'officer' regarding QI. The Pierson case is what was on my mind, just remember QI applies to all government officials, except the president and judges.
I used Wikipedia because they're often the best starting point when jumping into the rabbit hole of case law. They're not the know all but neither is really anything but the actual opinions. Good luck starting blind and digging deep using the opinions alone.
I suggest these 2 articles as a base to learn the concept of QI and dig as deep into the rabbit hole as you wish.
Best concise breakdown of qualified immunity I have found:
https://www.reuters.com/investigates/special-report/usa-police-immunity-history/
CATO Institute has some great info on QI. https://www.cato.org/blog/blatant-misrepresentations-qualified-immunity-law-enforcement
Pierson v Ray https://en.m.wikipedia.org/wiki/Pierson_v._Ray
Taylor v Riojas (the 2020 SCOTUS opinion on QI that I mentioned)
https://arizonastatelawjournal.org/2021/02/01/taylor-v-riojas-qualified-immunity-in-2020/