So the reason for keeping the commandments isn’t because of life after death, and if a person doesn’t want to keep the commandments then everything is fine?

What an Olympic leap!
First, just because it can’t be proven doesn’t mean it isn’t true. If you believe the tradition, that’s also a consideration.
Second, life after death seems very plausible to me, even if you aren’t convinced about the World to Come.
Third, the reason for keeping the commandments is not the World to Come, but truth and the duty to obey the Holy One, blessed be He.

1. True, but it’s rational not to believe it.
2. Scientifically, not philosophically, maybe.
3. True, but is a person who doesn’t keep the commandments eternally different from one who does keep the commandments?

Either you believe or you don’t. Philosophy and science are tools.
It depends whether you accept the eternity of the soul. If a person does not exist eternally, then he cannot be different eternally.

Is the Rabbi certain that there is life after death?

No. But I’m not certain about anything, not just about this.

What does life after death mean if there is no World to Come?

The persistence of the soul means that there is something non-material in us (soul, spirit) that remains after death.
What happens to it, and where is it? I have no idea.