I had this issue also yesterday, but I don't think it is related to installing 1Password 8 alongside 7. On iOS, after I've installed the version 8, I tried to log out from the version 7, didn't work, I just uninstalled version 7 completely. But in iPadOS, before installing the version 8, I first tried to log out, but that also did not work. I've ended up just uninstalling the app completely and installing version 8, same as on iOS. 🤷♂️
And is 1PW8 not available on mac appstore lilke it is on IOS appstore?
As far as I understood, desktop versions of 1Password 8 are packaged in a different way and yes, for macOS, it is not yet available on the App Store.