safari tries to open 10000 tabs

That could have been the result of loading an intentionally ill-mannered website.

Phony "tech support" / "ransomware" popups and web page - Apple Community generally describes those maliciously crafted attempts to convince you to do something in an effort to defraud you, but if you don't want to read all that, the easiest fix is to press and hold a Shift key when launching Safari from Applications or the Dock. That action launches Safari in windowed mode without loading its previously loaded windows or tabs.

Release the Shift key when Safari opens.

That should fix it.