The only guide I can see on the site is 4 years old by now, and seems outdated and half of it doesnt' even work now. I've been wanting to get into this game since i saw Dolfinh's former WR but i haven't been able to find any good resources. Is there some sort of secret discord?... Trying to follow the speedrun videos are about the best i've been able to do to no avail so far.
Welcome! The best way to get started right now is to join the Discord server (link in sidebar). That's where all the active Ecco runners hang out and we'll be more than happy to answer any questions you have about the game. Resources and guides are definitely a little outdated, but most of the run is fairly straightforward. I have plans of compiling a detailed guide in the future.
I would also check out Upthorn's excellent TAS (http://tasvideos.org/6789S.html). He goes more in-depth into all the various tech, and while not all of it is RTA viable it's a great way to learn about the underlying mechanics of the game.
I recorded a tutorial that goes over all the current tech as of August 2020. You can find it in the sidebar, or at this link: https://www.speedrun.com/ecco_the_tides_of_time/guide/opybf