I don't know if that's actually what it's called but it's when you use a potion/food while picking up a key item and skip the 'You obtained a thing' fanfare. Can someone please create a tutorial for this skip please?

I hadn't heard of this before but after some testing it seems to be done by using an item with an animation (potion/food) right as you pick up the thing. Possibly frame perfect, not sure, but simple enough that I don't think it really warrants a tutorial video.

Definitely not frame perfect; otherwise it wouldn't be consistent. Basically:
Have food/potion selected in your inventory.
On the 4th bounce for low ceilings or 2nd bounce for full jump space, do a full jump and start mashing L+R bumpers.
When you land on the item, you'll use the selected curative and the animation will be skipped.

Thanks for your help