Re: "Topics are kept for only three weeks and old topics are deleted"
You don't fool us, Google. Ad data is never deleted anymore, it just piles up higher and higher.
And we pay for the service..
"Topics are kept for only three weeks and old topics are deleted. Topics are selected entirely on your device without involving any external servers, including Google servers. When you visit a participating site, Topics picks just three topics, one topic from each of the past three weeks, to share with the site and its advertising partners."
So it seems to rely on something local. Because AlphaGoo takes users privacy very seriously, presumably this means Chrome users can pick About:Topics and display the topics AlphaGoo has selected for them. If that shows Topic has decided you're most interested in hazlenuts, you'll get one in every ad. If the user disagrees, they'll easily be able to alter their preferences to reflect their actual preferences.
So a few weeks ago, I was looking for a new washing machine. This involved some searches for most reliable brands etc. For that week, it would have been one of the more active search queries. Now, the washing machine is sitting in my kitchen, so trying to sell me another one is pointless. If I could demote that interest in Topics, this may actually be useful.
For more sophisticated users, there will obviously* be a simple .xml file I can edit directly, or through a convenient app so I can express my preferences and see ads for stuff I might actually be interested in. Or I could delete it, set it to read-only, or do all the file things a device owner may reasonably be expected to be able to do with their own device and their own personal data. I mean I might not want my searches for 'Breaking strain of a scrotum', or 'Best ways to hang an ad exec by their nuts' visible to the whole world. Or maybe I do, and someone has produced such a device.
*Who am I kidding? It'll be encrypted and obfusticated 'for security'. But if it is local, it gives me hope that it can be manipulated or disabled. Hopefully in a way it can benefit the user.