What is this? Is the online version is not the latest one, actually 5 version difference between the online and offline version?
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?
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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.