Your installation is also tied to your Avast Account as would be any paid license/subscription.
Inadvertently when joining this forum you would have signed in via that same account.
I don't use Avast One, but in Avast Antivirus Free Right clicking on the Tray Icon > Registration information - that opens the UI and you can Select the Go To Account (xxxxxxxx.avast.com). Now that account should still be present after uninstalling avast, so you would have to link the new installation to that account/registration/license, etc.
See attached images (click to expand), whilst these will be different for Avast One, in essence it is the same.