I understand your frustrations. Agile is really lean manufacturing applied to software development. The key is End-to-End Test Automation and Continuous Testing, somewhat like quality control and production pipeline in other engineering. However, E2E test automation is neglected in most software teams. IMO, 70% of all SDLC shall be test automation related. I have practiced this discipline for over a decade, the great benefits are hard to describe in words (I wrote many articles, still a lot more). The proof is large scale software I solely created, mostly in my spare time.

Real Agile works, but extremely rare; Most are doing fake Agile. The easy way to tell fake Agile is to check E2E test execution in a CT/CD server. When there so no check (automated E2E via UI regression testing), the manager, agile coach, architects and senior engineers will spend useless or negative activities, such as trying new hype architecture (e.g. Microservices), meetings, bringing in various silly processes, such as mandatory PR code review process, estimating user stories, ..., etc.

ThoughtWorks is a good case study. It started with a heavy emphasis on E2E test automation: Watir, Selenium, WebDriver, and CruiseControl were all created by ThoughtWorkers. This paved a good reputation for TW to grow. Then, E2E test automation was neglected, and see the current situation now.

I recommend Mary Poppendieck's book: Implementing Lean Software Development: From Concept to Cash.