What is this? Is the online version is not the latest one, actually 5 version difference between the online and offline version?
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Look at the releases page. There are newer beta releases. Every couple of months the latest update is transferred to a stable update, and then a new beta cycle begins again.
So the online editor uses only stable editions, right? Is there any "latest version" edition of online editor even if it is beta?
editor.construct.net serves the latest stable release.
editor.construct.net/beta serves the latest beta release.
You can set in the settings (https://www.construct.net/en/make-games/manuals/construct-3/interface/dialogs/settings) whether to use stable or beta channels.