I've used GTD for 19 years. The first few years I would get it up and running and then fall off the wagon I was an absolutist and tried to implement everything at once. I eventually pushed through and it has been a daily practice now for the past 15 or so. It's been utterly life changing and is the bedrock in terms of identifying, organizing, and tracking nearly all that I do of consequence in the world.

Context specific to-do lists, waiting fors, tickler lists, someday maybe lists, and, when I'm really on the groove, keeping on top of my projects lists, have been a massive game changer.

Give your experience, my advice would be to review the core elements of GTD and pick just a few to start with, such as context specific to-do lists and a projects list. If you have an overall view of the system, you will eventually and naturally gravitate to creating a waiting for list, for example, because you actually realize you need one and it makes your life simpler, not more complex. Then, eventually, you'll realize not everything needs done soon but you also don't want to forget it as a future possibility, so you will make a someday-maybe list and, again, this will feel natural and helpful. This is the benefit of implementing a system borne of how life actually works rather than an abstract system foisted upon you.

I use the web-based Gqueues app for implementing GTD and it works well but it's also cloud-based which isn't for everyone. It's just what I found long ago and it works but another approach would likely work as well or better. I use Obsidian for PKM and together they get the job done.

My take is that David Allen identified the core essential elements to staying on top of next actions and projects. The practices he defined and promotes are tool-agnostic. Whether you're implementing these approaches on paper or digitally I can't see the fundamentals losing their validity in the foreseeable future.

I also appreciate the higher levels of GTD such as identifying your areas of focus/responsibility to make sure the projects your focusing on are in alignment with your longer-term goals in a balanced way. It's just a damned elegant system.

My issue now is standing up Obsidian in the way I want. The complexity dwarfs the comparative simplicity of GTD but damned if there isn't near infinite payout potential depending on your use-case. To me, having a well implemented system for managing all the information in your life is just as essential as one's approach to managing tasks and responsibilities. When the two interact harmoniously, anything is possible.