The Block Sites custom filter can be used to prevent Safari from loading any website or link. Once you add and enable a rule containing a specific site's name to Block Sites, Safari will refuse any connection attempts to such a site.
How to block sites
On iOS:
Launch 1Blocker.
Go to Custom Rules > Block Sites.
Tap the (...) menu in the upper-right corner and choose New Rule.
Choose a name for your rule (optional) and add the domain to block.
Both variants with and without the "https://" part are valid.
Tap Save.
On macOS:
Launch 1Blocker.
Go to Custom Rules > Block Sites.
Press the New Rule button in the (...) menu at the top.
Choose a name for your rule (optional) and add the domain you want to block.
Both variants with and without the "https://" part are valid.
Tap Save.
If you want to quickly access a site blocked by 1Blocker, you can load it without content blockers. Learn more here: Deactivate content blockers in Safari.