error 404, website not found, also when logging into different accounts, page refreshes and loggin data lost

Any add-on VPN client apps or add-on security apps or add-on ad-blocking extensions in use?

If so, discontinue, remove, and try again.

The phrasing of your reply is ambiguous.

No VPN installed, or no VPN in use? If there is a VPN app installed, remove it.

The Safari pop-up blocker is unrelated to an ad-blocker app. If you have an ad-blocker extension, remove the ad blocker app.

Any other add-on security apps or service or filters installed?

Once those have all been removed, test again.

Add-on anti-malware tends to be problematic, at best.

Some of the well-known add-ons have had surprises, too.

I’d not be surprised to learn other add-on apps acquire and market similar data.

The built-in anti-malware does well for most uses.

Including blocking corruptions that some add-on anti-malware has attempted.