If you would like to block only one room, you could set up Out of Order or House Use for this space. Once the space is Out of Order or House Use, it is no longer available for booking. You can see the difference in how these two features influence your availability here:
How to set it up?
House Use: the house use feature is intended for internal use (showroom, training, friend, employee, etc.).
You can create a House use from the Timeline. In the top right corner, click on the House icon.
Here you can select the Block name (usually, the reason for the House Use), the room number, and dates.
Out of Order (OOO): an OOO is intended to block a room from being sold for a prolonged period of time. It is usually used for major repair or similar actions.
Click on the space number in the Timeline:
Navigate to Out of Order in the top right corner:
Here you can select the Block name (usually, the reason for the Out of order), the room number, and dates.