Go to the Extend and enable "Layout Builder Restrictions" module.
Go to Structure -> Content types -> From operation column click on the dropdown arrow of required content type -> click on “Manage display.”
Here you will see two different layout option
A. BLOCKS AVAILABLE FOR PLACEMENT (ALL LAYOUTS & REGIONS)
Once you open this option, you will see options to blacklist/whitelist/show all block for each and every available block.
Here, you will get 3 options for each block type.
i) Allow all existing & new <block types> blocks: To get list of all blocks.
ii) Allow specific <block types> blocks: To whitelist the blocks.
iii) Restrict specific <block types> blocks: To Blacklist the blocks
B. LAYOUTS AVAILABLE FOR SECTIONS
Once you open this option, you will see the option to restrict layout.
Here, you will see 2 options to restric layouts.
i) Allow all existing & new layouts: To get a list of all available layouts.
ii) Allow only specific layouts: To whitelist the specific layouts.
As we can restrict any block(s) or layout(s), this helps the content editor or site builder to focus on only important/needed block(s) or layout(s).
If any website has lots of block(s) or layout(s) which are not in use, then this module is the best option to restrict block(s) or layout(s).