1. Backup, launch App Store and update macOS to the latest version.
2. If Safari is slow, stops responding, quits unexpectedly, or has other issues
https://support.apple.com/en-us/HT203353
Disable all extension and test.
Section: Manage Extensions
https://support.apple.com/guide/safari/use-safari-extensions-sfri32508/mac
3. Try Safari Technology Preview to download items from internet.
This is another self standing beta version of Safari.
https://developer.apple.com/safari/technology-preview/
4. Sometimes third party software can cause this kind of a problem.
Please run EtreCheck and post the report here.
https://etrecheck.com
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.