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If you go to this page: Release Release 1.8.19 Security hotfix release · arduino/Arduino · GitHub
You will see something like "12 commits to master since this release". If you click on the "12 commits" link you will see a list of all commits since the last release.
If the latest commits were made very recently then they might not yet have been included in the hourly build download.
You can also find a list of the major changes here: