I have a outdated master branch which was updated back in 2020.

Now i want to sync my master branch with latest release branch, I tried below

git checkout master
git merge release

Here merge happens with fast-forward method and 1000+ files got changed/added.

Since here merged happened with fast-forward method can i be sure that all the code present in release branch is now in master branch (master does not have anything extra and is exactly same as release) or there could be any scenarios where my master is still not in sync with release?

Note: I want all code from release to master as release has latest code and trying to avoid re-write history option.