You can block specific Chrome/Brave/Vivaldi/Arc URLs by editing your block and adding the URL like chrome://extensions under the websites tab.
If using Edge, you can add a URL like edge://extensions under the websites tab.
If using Firefox, you can add a URL like about:addons under the websites tab.
Blocking these URLs won't display the block page. The tab will be closed and a notification will be displayed instead.
SPECIAL CASE #1
Adding * to the websites tab will not include browser URLs. Most users do this to block all websites, not thinking it technically applies to browser URLs as well.
If you also want to block all browser URLs, you should add chrome://* or edge://* or about:* instead.
SPECIAL CASE #2
Adding chrome://* or edge://* or about:* will not include the newtab, extensions/addons or welcome pages.
To block these, you will need to specifically add it in like: chrome://extensions or about:addons.