Event Viewer clear logs – and how to see if laptop has been used

Dear all

When I press the power button on my laptop, it get logged in Event Viewer i Windows.

That way I know, that the laptop has not been turned on by others than me.

Then I saw, that it is possible to clear logs.

1.
What happens to cleared logs in Event Viewer – are they completely gone?

2.
Other ways to find out, if the laptop was turned on by other than me?

Thank you