How does the xenomorph get on the Covenant? Theories accepted

well, depending on where on the hull it's lurking or tucked into, they could plausibly miss it.

and given what we know from the movie ALIEN itself, you can blast a grapple into one, kick it into hard space vacuum and it'll still be functional and interested in getting back to the prey inside...so yeah, survival in space for a reasonable duration is NP for them.

Blackwinter-witch that is possible. I wonder if someone helped the Xeno get there, or it it was smuggled in an infected person

joylitt

ALWAYS a possibility...Humans can do the stupidest things if they somehow think there's some huge benefit involved.
The sticking point my brain keeps tripping on is after the events with the neomorphs and the blown up Lander, they'd likely be pretty cautious in picking folks up with that flat-deck ship...OR, the Covenant lands, which then opens up many more possibilities for the critter to gain entry.

Well this is the interesting thing..

I would assume its via one of TWO Methods.

1) There is a surprise person who has a Agenda regarding the Specimen.

2) The new take on the Alien's Rapid Life Cycle will be the explanation.

Or Alternatively the Xenomorph just hitches a ride... which i think wont be happening.

Oram and facehugger?

Damien Birch, the mexican gay guy, carries it his body.

I doubt it's Oram, because he seems to birth the first xeno under the watchful eye of David.

There was a brief shot of something (I assume a xeno) trying to break out of a cockpit window (out, not in), so perhaps it stows away on the lander, is taken to the ship, then breaks out of the lander cockpit window to get into the main ship.

I'm guessing it hides somewhere on the lander, who knows lol

the rescue ship has one on, which daniels is trying to deal with as they are leaving.

another one inside a crew member i would guess?

the area where they are playing cards looks similar to where we seen the xeno, lurking behind the flaps. 

this is set at the end of the film, the mood of the shoot, the lights you get the feel this is at the end.

im thinking they maybe get one xeno  and think its over, then another appears?