Go step by step and test.
1. Click in the menu bar and click Force Quit.
Launch Safari holding the shift key down.
2. If Safari doesn‘t load a page or webpage items are missing
3. Enable Develop menu and Empty Caches
4. Turnoff or uninstall extensions and test.
Section: Manage extensions: https://support.apple.com/guide/safari/use-safari-extensions-sfri32508/mac
5. Remove cookies and website data.
Manage cookies and website data:
6. Sometimes third party software can cause this kind of a problem.
Please run EtreCheck and post the report here.
Download it, open Downloads folder, click on it to open and select ”Open”.
Select a problem from the “Choose a problem” popup menu box, and then “Start EtreCheck” in the dialog.
Click “Share Report” button in the toolbar, select “Copy to Clipboard”, and then paste it when you reply.