Hello iPopescu,
Welcome to Apple Support Communities!
If we understand your post correctly, Safari crashes when trying to bookmark a certain website. We'd like to help!
Let's try clearing browsing history to see if this will now allow you to bookmark that site in Safari.
Clear your browsing history in Safari on Mac
1. In the Safari app on your Mac, choose History > Clear History, then click the pop-up menu.
2. Choose how far back you want your browsing history cleared.
We also recommend starting in safe mode. Sometimes just starting in this mode and then restarting can resolve issues like this: How to use safe mode on your Mac
You can also create another user on your Mac and test to see if you experience the same issue.
Set up users, guests, and groups on Mac
Let us know if you have any questions.
Thank you for using Apple Support Communities.
Take care!