Agee: "doesn't feel right". (And thank you USAFRet for testing the Powershell script.)
I was looking into some way of reverse engineering the OP's issue. Mostly dead ends but someone with more Powershell experience would likely to be able to set up the necessary logic that checks for a registry key, a service, etc. and if found "on" just turns it "off" again. I.e., button goes back to off again.
Regarding: " I check updates, it says I have to update Windows Antivirus."
What is the exact wording and how is the message presented?
One solution is just not use defender and instead us a 3rd party Antivirus like Bitdefender Free whbich will update itself every hour and leave you alone. I use Bitdefender Total Security and it doesn't even bug me for anything. Always in top 3 of AV in tests so its not a bad option.