What is the difference between LRT and RTA? And why is the LRT time always (or almost) the same or less?

RTA stands for Real Time Attack. This basically means the total time you take from the moment you start your run to the end of it, including moments where the runner has the game paused or is dead. LRT stands for Load Removed Time. This is the time of a run that is used to actually time the run. It removes moments where the game is paused or you are not in current gameplay. You don't have to time this yourself because livesplit has an autosplitter that you can use by typing in poppy playtime chapter 1. Usually runners don't spend that much time paused so that is why the times are pretty similar.

you can put it on your livesplit :)

go to "edit layout" on the big plus and "timer" and take "detailed Timer"