What it covers

Your reading is correct. All of these examples fall under the Use an Object action. The wording is very clear:

Use an Object (PHB p. 193)

When an object requires your action for its use, you take the Use an Object action.

As Eric pointed out in a comment, the Thief Archetype for the Rogue gets to Use an Object as a bonus action. They would be able to poison, drink potions, or spread caltrops as a bonus action.

What it does not cover

Activating a magic item does not use the Use an Object action.

Activating an Item (DMG p. 141)

If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.

What it covers

Your reading is correct. Two of these examples fall under the Use an Object action. The wording is very clear:

Use an Object (PHB p. 193)

When an object requires your action for its use, you take the Use an Object action.

As Eric pointed out in a comment, the Thief Archetype for the Rogue gets to Use an Object as a bonus action. They would be able to use poison or spread caltrops as a bonus action.

What it does not cover

Activating a magic item does not use the Use an Object action, so drinking or administering a magic potion cannot be done via the Use an Object action.

Activating an Item (DMG p. 141)

If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.

What it covers

Your reading is correct. All of these examples fall under the Use an Object action. The wording is very clear:

Use an Object (PHB p. 193)

 

When an object requires your action for its use, you take the Use an Object action.

As Eric pointed out in a comment, the Thief Archetype for the Rogue gets to Use an Object as a bonus action. They would be able to poison, drink potions, or spread caltrops as a bonus action.

What it does not cover

Activating a magic item does not use the Use an Object action.

Activating an Item (DMG p. 141)

 

If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.

What it covers

Your reading is correct. All of these examples fall under the Use an Object action. The wording is very clear:

Use an Object (PHB p. 193)

When an object requires your action for its use, you take the Use an Object action.

As Eric pointed out in a comment, the Thief Archetype for the Rogue gets to Use an Object as a bonus action. They would be able to poison, drink potions, or spread caltrops as a bonus action.

What it does not cover

Activating a magic item does not use the Use an Object action.

Activating an Item (DMG p. 141)

If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.

What it covers

Your reading is correct. All of these examples fall under the Use an Object action. The wording is very clear:

Use an Object (PHB p. 193)

When an object requires your action for its use, you take the Use an Object action.

As Eric pointed out in a comment, the Thief Archetype for the Rogue gets to Use an Object as a bonus action. They would be able to poison, drink potions, or spread caltrops as a bonus action.

What it does not cover

Activating a magic item does not use the Use an Object action.

Activating an Item (DMG p. 141)

Activating some magic items requires a user to do something special, such as holding the item and uttering a command word. The description of each item category or individual item details how an item is activated. Certain items use one or more of the following rules for their activation.

If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.

What it covers

Your reading is correct. All of these examples fall under the Use an Object action. The wording is very clear:

Use an Object (PHB p. 193)

When an object requires your action for its use, you take the Use an Object action.

As Eric pointed out in a comment, the Thief Archetype for the Rogue gets to Use an Object as a bonus action. They would be able to poison, drink potions, or spread caltrops as a bonus action.

What it does not cover

Activating a magic item does not use the Use an Object action.

Activating an Item (DMG p. 141)

If an item requires an action to activate, that action isn't a function of the Use an Item action, so a feature such as the rogue's Fast Hands can't be used to activate the item.