How can I get rid of update notification at start?

[fenInfo]

“update_check”: false //doesn’t work.

[OdatNurd]

The update_check setting is only consulted and used in a licensed copy of Sublime, so in order to use it to block the update dialog you need to purchase a license, or add your license if you’ve bought one but haven’t told Sublime about it.

Other than that it should work, so if the title bar of Sublime doesn’t say (UNREGISTERED) then I’d verify that the setting is in Preferences.sublime-settings in your User package (e.g. in the right hand pane when you choose Preferences > Settings from the menu) and that Sublime doesn’t generate a warning when you start it that it can’t load the preferences.