It's no secret that there are groups actively looking for new exploits and that sometimes vulnerabilities are discovered that become zero days. It's a good bet that police and security services take an active interest in those vulnerabilities when they are found.
But that's very different to claiming the police can easily unlock any device any time they want to and there is a range of private companies around who provide that service to them.
The manufacturer provides the means to bypass many of the cheaper tools, but few people use them.
There are more exotic tools that can bypass security controls. These are more niche and not generally available to law enforcement. There may be some crossover when counter-intelligence interfaces with law enforcement. (Ie. FBI, DEA, RCMP, ICE, etc)
Yes they do. Now name one that works consistently against a fully patched modern iPhone.
"As with all of the other information these companies store for or about their users, because Apple and Google deliver push notification data, they can be secretly compelled by governments to hand over this information," Wyden wrote.
Then there are all the ways, both white and varying shades of gray, of installing software in the end devices. That's your primary threat right there.