This slime glitch can no longer be made from the corner of the block in which it is shown in the image, there is a technique to make that slime glitch that I made in my current speedrun, first you must position yourself in this position where it is located in the image:

Once positioned you have to advance a little once you are crouched, then you have to do a jump of 0 ticks (that is, a jump by pressing the "SPACE" and "W" key at the same time), or you can use the technique of inventory, a Once you have jumped, turn to the corner of the block shown in the image:

And finally you have to land in the corner of the slime and press the crouch key, if you want you can see this video here: