Google is indexing more pages but impressions are going down

A client of mine has a huge website, millions of pages, which has been live for a numbers of years now. Due to the nature of the site, pages have very thin content.

When I started working on the account, the majority of pages had been deindexed due to Google choosing a different canonical or the server being not responsive or too low.

Over the past months we have been working on those issues and they now have an increasing number of indexed pages. However, the number of impressions and clicks is going down.

Core Web vitals and the server are now OK, and we are fixing the issues with the thin content and wrong canonicals. Is it just a matter of time or is there something I am missing?