What is the secret ending of Black Mirror: Bandersnatch?

I've not seen the secret ending myself, but according to refinery29:

The secret path involves Stefan interacting with Jerome F. Davies (Jeff Minter, a real video game designer), the author of Bandersnatch.

According to popsugar:

The Davies cameo is actually very short and jarring. Stefan awakes at his computer, a bit confused and out of sorts. He stands and turns around, and that's when he sees Davies, if only for a split second. That's because the crazed character is charging at Stefan. Before you or Stefan have time to register what's going on, Davies collides with Stefan, stabbing him in the stomach. (What the hell, Davies?! I thought we were on the same team!) This, of course, is a dream, and the impact of the stab is enough to jolt Stefan out of his slumber. He's back in bed, and it's morning. We're rerouted back to the point where the previous through-the-mirror time travel dream ends, and the story continues on from there.

As for how to get to the secret ending, I found this on TV Guide:

Frosties (cereal) > Thompson Twins (music) > Refuse (to accept job) > Yes (to talk about Mom) > No (forced choice, not going with Mom) > Phaedra (vinyl selection) > Shout at Dad > Visit Dr. Haynes > Yes (to talk about Mom) > Nails > Flush them (medicine) > Hit desk > Pick up the family photo > Destroy computer > White Bear symbol (over Netflix) > Kill Dad > Bury the body > Yes (it'll be ready) > Let him go (Colin) > back to Chop or bury > Bury the body > back to Chop or bury > Bury the body > back to Chop or bury > Bury the body > back to Chop or bury > Chop up the body > Throw tea over the computer > back to Follow Colin > Yes (take drug) > Colin (jumping over the balcony) > Pick up the family photo ...

There is a super secret ending which contains a guide on how to download a playable copy of Nohzdyve for the ZX Spectrum.

In order to get this ending, take the following path:

Sugar puffs, Thompson twins, Accept, Accept, Go back, Refuse, Yes, No, The Bermuda Triangle, Shout at Dad, Visit Dr. Haynes, Pull Earlobe, Take them, Follow Colin, Yes, Stefan, Go back, Colin, Flush them, Hit desk, Pick up book, PAC, Throw tea over computer, P.A.C.S., 20541, Who’s there?, Netflix, Try to explain, Tell him more, Fuck yeah, Fight her, Kick him in the balls, Who’s there?, White Bear symbol, Back off, Kill dad, Bury body, Yes, He jumped, Chop or bury?, Chop up body, Destroy computer, Pick up photo, White Bear symbol, Chop up body, Destroy computer, Get rabbit from dad, PAX, White Bear symbol, Chop up body, Destroy computer, Get rabbit from dad, Toy, Yes

Source: Black Mirror: Bandersnatch Super Secret Ending | Game Within A Game