By default Solus MATE has org | mate | power-manager | action-sleep-type-battery set to hibernate instead of suspend by default.
So if you enable 'put computer to sleep when inactive for X minutes' in the mate power settings | battery tab, your machine will hibernate instead of sleep after the idle time.
Most other linux desktops suspend on idle and not hibernate on idle (e.g. this is how Solus Gnome and Budgie behave), so this is kind of unexpected for a default behavior. Also, to change the behavior you need to do it through dconf which new users won't know how to do.
I would suggest setting this to 'suspend' by default instead. IMO this is the default behavior that most users would be expecting.
Note: There is an upstream issue for this as well: https://github.com/mate-desktop/mate-power-manager/issues/183