As per title, I can't seem to figure out how to change it to be true by default. Will be thankful for suggestion.

Edited January 13, 20223 yr by PatrickRQ

This is set by the Members automatically follow content they... setting under Notifications > Followed Content in the ACP:

 

Members can change this setting themselves in their notification settings, or when creating new content. It’s not possible to force this setting to always be on, except by creating a plugin and hooking into the relevant code.

Edited January 13, 20223 yr by Runar

Thanks @Runar. I saw that, what I missed was to reset members preferences to default, this is why I could the change.

2 minutes ago, PatrickRQ said:

Thanks @Runar. I saw that, what I missed was to reset members preferences to default, this is why I could the change.

That's true, you can reset the notification preferences for everyone to your new default. But keep in mind that anyone can change this setting for themselves at any time, so you shouldn’t rely on resetting their preferences.

I believe the question you are asking is how to reset peoples existing settings. You can click the "Reset All Members to Default Preferences" button in the top right of that screen.