They’re two different tools that operate differently.

First, they don’t trigger at the same time. GSC fires on the SERP and GA fires on page load. Second, clicks and sessions are not the same thing. A click is a click. Session has a time element to it. The definition is not nearly as straightforward as it seems. Third, the data is unstable in both tools for a few days. Personally, I give it three days. Fourth, GA may be using sampling. Look at the shield at the top. There’s a color code, but I can’t remember it off hand. Hover over it and you’ll get a tool tip telling you.

Bottom line, these are two different tools that measure similar things, but not the exact same thing and they operate differently. There will be differences in the data.