Open a Search Console comparison and a falling average CTR looks like a problem. In isolation it can be. Next to a large jump in impressions, it usually means something else entirely: the site started ranking for queries it was not competing for before.
Why CTR falls when SEO is working
A new, broader set of impressions dilutes the click-through rate even when clicks are rising in absolute terms, because the site is now showing up for higher-funnel, more competitive queries that convert to a click less often than the narrow branded terms it used to rank for exclusively.
On one account, average CTR read lower after six months of work, 1.3% against 6.5% previously, while impressions grew 25x and clicks grew 5x over the same window. Read alone, the CTR line looks like a regression. Read against impressions, it is the site graduating from a small set of branded terms to competing on broad, high-volume queries, which is the trade you actually want at that stage.
The fix is to read metrics together, not alone
Impressions, clicks and CTR move as a system. Judging any one of them without the other two is how good SEO work gets reported as a decline.