(adsbygoogle = window.adsbygoogle || []).push({}); can this be done in solo mode.

No, it will let you get to the last step but won't let you on the plane. You can do it with two or more people only.

Proof:

I'm pretty sure it was that video but there was a top comment a while ago, and it mentioned that Spider was on Easy difficulty because the last guy wasn't a runner and easter eggs cannot be done on Easy. so it maybe could

No, it can't, many people have tried. Don't believe me go try it yourself.