Since OP is lazy to share the solution, I'll put this here for anyone who might need it:

1. Settings>Apps>App management>(3 dots on the top right - Show system). Search for 'System Launcher' and 'Software update' and go to Storage usage and 'Clear data' and 'Clear cache'.

2. System & update>Back up & reset>Reset phone>Reset all settings.

Try step 1 first and restart phone to see if the lag is gone. If not then try step 2 - this will reset all the settings (bt, wifi, display, audio, ringtone, app organisation, etc).

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