If u want 1 a bit earlier u can actually trade metall or whatever the others want for a fertilized rex egg. Its ideal temperature is between 32-34 degrees. If u have no chance to get a kairuku, a dimetrodon or some air conditioners u can go to an area woth the required temperature (press h to see the temperature). The egg doesnt lose the hatch progress and if the temperature isnt good anymore u can put it in your inventory and it wont lose health. After i hatched u have to feed it by hand untill its grown to 10% (if u go to its inventory u can see how much it will be able to carry when its fully grown and how much it can carry f. e. if it will be able to hold 350 weight its grown to 10% when it can carry a weight of 35). After that it can just eat out of the feeding trough. After 4 days u got yourself a rex (u have to refill the feeding trough regulary since freshies starve fast and meat doesnt last very long). U can also do that with a giga but it takes almost 2 weeks.....
So my experience with this beast was horrifying but I knocked it out it took so much tranq arrows it took 30 tranq arrows and I ran fast with the Brontos because there were lots of dinos with the brontosaurus then it was attacking the other dinos then I shot it a lot then it fell asleep because the thing it was attacking a a tank it was an ankylo so that’s my experience with a rex.
Just tamed one I will tell you my experience, so I found one and shot it with tranc DARTS (but tranc arrows work just as well although you need a few more :)) and it kept on getting deststracted by other Dino's which made it not attack me, so after I knocd it out I killed the other animals attacking the unconchis body with my Pump shotgun and gave it raw meat and a couple of bio-toxins and boom I got Rexy I hoped this helps on your next Rex tame
I recommend using a scorpion to tame it, pump all levels into health on the scorpion. Then just attack the Rex but with 10 to 20 seconds in between hits, DO NOT pump anything into dm. Also this is what I use to tame literally everything, and it doesn’t even cost anything. Pls put this up in chat for everyone to go “oh that’s not a bad idea” 👌😄👍