Everyone either goes silent or describes an idealized architecture that has glaringly obvious flaws in regards to meeting business goals.
I think maybe the top ten companies in our industry do this at scale well enough to work. Maybe.
2) subscribe to a service that alerts on vulnerabilities in the assets listed in 1). Run Nessus scans. License cost you a bit over $1k a year.
3) invest in a resource to maintain the register and respond to alerts. Tie them into a governance model so management are aware of risks and can divert time and money when needed to mitigate
Security is a process not a technology. Nothing I've mentioned here is sexy or advanced.