So here's what I got. I had to fire up the old Xbox-1 for a few of these, but I found the rules are the same for Java-Edition and Bedrock-Edition:

Soul Sand and Soul Soil

These blocks will change behavior drastically when the player is wearing boots enchanted with any level of the Soul Speed enchantment. When these requirements are met, they will speed the player up, rather than slow them down (for Soul Sand).

Slime Block and Bed

Both of these blocks will normally make a player bounce when falling onto them, but if the player is crouched whist falling onto one of them, it will behave as a normal block and administer the same amount of fall damage as usual.

Scaffold

The Scaffold will allow a player to walk on top of it, but if the player crouches they will start to descend.

Powder Snow

If a player is equipped with Leather Boots, they will not fall into the Powder Snow but rather walk on top of it.

Ladders and other climbable blocks

Ladders will normally move players down if they are not pressing the Jump key, but if a player crouches it will allow them to ascend the Ladder, but not descend.

Interactive blocks (Chest)

Any block that the player can interact with, such as: Chest, Crafting Table, Furnace, etc., will only allow a player to use it if they are not crouched. Otherwise it will act as a normal block and allow placing of other blocks on it.