You've probably already tried this, but TrizULTRA + Keto flush worked wonders for my dogs persistent ear itching.
https://www.chewy.com/trizultra-keto-flush-dogs-cats-horses/dp/126809
Just squirt in a bunch of the liquid, massage behind the ear for 30 seconds, let your cat shake its head, then wipe the ear with a clean soft towel. Do that daily for a week and it hopefully will make a big difference. Then you can do the rinse weekly or even monthly after that to maintain.
Ah yes, Ronald Reagan, staunch proponent of a right to abortion and gay marriage.