I see that runners even using emulator can do this part in 2:28 and I never can.

Maybe because I'm a beginner I can't identify the problems in my way of playing...

Could someone who understands help me by watching this short video I recorded?

Hi you have to slash your sword AFTER entering the keyguard 2 room. This gives the guard more time to be lower. Also you need to align yourself directly under the statue/chest. Download the practice hack if you haven't already to grind the rooms that cause you trouble.

For further in-depth info on certain rooms check out the FMG Tutorial on youtube. It can really help a lot if you are in trouble.

You are missing the most basic movement strats. at 1m42s in the video, you are moving up then right into the door, instead of straight up-right. Same at 1m47s. I'm not gonna watch any further, but I guess this will be happening a bunch of more times.

Speedrunning is about taking the shortest path possible, and in this case, you don't even need glitches, just math