How do I reinstall Safari on my iMac?

Here you go. While it says it will not affect your apps or data, I would still have a good backup in case something goes wrong.

How to reinstall macOS - Apple Support

If there is something on your Mac that is conflicting with Safari, reinstalling the OS won't resolve that problem. You would need to remove the app that is causing the conflict. Review these categories of apps that should not be installed on your computer and have caused conflicts with the Mac OS including Safari:

• Cleaners
• Optimizers
• AntiVirus
• VPN

The other step of resetting the Mac to Factory Settings will wipe everything off of your computer, but does reset your Mac to what it would be like if it was just purchased. Restoring from a backup after this may simply load the problem back to your computer.

Erase your Mac and reset it to factory settings - Apple Support

Again, this is a drastic step for an issue that is usually easily solvable if we knew what the problem was. You can post the free EtreCheck report using the Additional Text option when posting that will provide a snapshot of your computer that may reveal the problem and does not show any personal information.

Using EtreCheck - Apple Community

Reinstalling Safari involves putting your Mac into Recovery to do a complete OS install. This is usually never needed and given the problems you may be experiencing with Safari, we would likely be able to provide a solution for you that does not include this heavy-handed approach.

Here you go. While it says it will not affect your apps or data, I would still have a good backup in case something goes wrong.

How to reinstall macOS - Apple Support