But it's not, only in certain cirumstances.
One of which is "commits a foul or handles the ball to interfere with or stop a promising attack". Did Mane do that? Hardly, as Palace didn't actually have the ball. They would have got posession if Mane hadn't handled it, but the ref has to decide if he handled it to stop Palace having a promising attack, or if he did that thing that players do every game (and i believe had already happened earlier in this game with no yellow card shown) of grabbing hold of the ball after believing they were fouled. Doing that isn't specified as a yellow card offence.
See above.
Obviously if this had happened in a Huddersfield/Swansea game the ref would be praised for using common sense and not ruining the game by sending off a player for something that happens every game, but as it benefitted Liverpool it's all part of a massive conspiracy on behalf of them and the rest of the "sky 6". Totally ignoring the only reason Mane being sent off was being discussed was because he was booked in the first half when he should have had a penalty, probably still booked as well but the penalty should still have been given. And he had a goal disallowed, which goes against any conspiracy doesn't it, no VAR so they could easily have let it stand.
Oh yeah, forgot Mane not being suspended against us was part of the conspiracy too, cause him playing is the reason we won't win next weekend. A proper conspiracy would have sent him off, watched his replacement smash us next week and give him a rest before the CL second leg game against City.
In spite of all the ifs, woulds and shoulds analysis, it would appear that Jurgen Klopp expected him to be sent off too according to a quote on here. I didn't watch it so couldn't possibly say/guess or defend the missing yellow, but it suggests that the ref was wrong when even the manager gives a straight cough.