Thanks to the previous solutions. This was a good place to start but I had to work out a whole lot of stuff for myself still after getting into debug mode. The HAP seems to be very glitchy and would not register achived pages most of the time.
For this achievement, you need to get to the HAP and fill out all the achives so that all four dates at the top show 100%. Once you get 100%, a file will download which you can open and it will take you to a Zone with three developer shout out pages.
To get to the HAP HAP - Hypnospace Archive Project
Keep playing the game until you are in the modern times and the date is your current IRL date.
You will get an email with a download of the HAP which you can download and install
Getting to Debug Mode. As stated before, load up the game. You may need to quit from the Xbox guide and load up again (Make sure to log out of HypnOS to save your progress and not get the Mr Resetti warnings). You will need a keyboard and mouse plugged into your Xbox to do this, I only have one USB slot on my machine, but I was able to get it working with a multi USB adapter to plug both in at once.
Load the game and let the developer logos go by, and you'll get to the press any button screen. Immediately after that, a bunch of text will scroll on the screen like an old school computer load screen. This is when you need to hold D E B keys on keyboard. Keep it held and you will skip ahead to the load screen. Load up your game in the XX XX 20XX date and install HAP if you haven't already.
Filling out the ArchivesOpen the HAP, you will be greeted with a bunch of rectangles, in the current date archive, there's only a few, but hundreds in the other three dates. Each rectangle is a Hypnospace page and all of them (hundreds) need t be not just opened, but correctly archieved and turned blue.
-Yellow rectangles are already captured by other HAP users and you don't need to worry about them
-Red/hashed rectangles are pages you have not yet found. If you activated debug mode correctly, hovering over these will show a page description, holding Shift and clicking them will open the page.
-Blue rectangles are pages you have captured. Once blue, you don't need to worry about them again.
Terry's Worm PageI recommend getting this early as the page consistently crashes the game. You don't want to lose a load of progress because you accidentaly picked this page from the HAP and crashed. It is possible to archive it despite the glitch. Save your progress by logging out and logging back in before you try this.
Open the browser and search for the word WORM. The page exists on November 5th and 26th only. You will get one hit for Terry's worm page on each of the first two dates. When you load it, you will see the page for about a second before the page glitches and crashes the whole game and kick you to your Xbox homepage. You will want to load it for half a second then hit the back button. I had to do it a few times as the page was not registering on the HAP. Make sure you have it registered for both dates and save your game. You generally know it has registered right as when you load it the HAP logo in the bottom right will stop spinning.
Filling the ArchiveFirst off, my general method for going through the pages. You can open a page from the HAP menu with Shift+left click, there will be a small window called CAPTURES, and I would cycle the three dates with the PREV and NEXT buttons to get the same page as it appeared in all three dates. If you get page not found error, it can be ignored as not existing at that time.
Note that some pages require the Dreamtoolz app to run the page in safemode, or reload the page if the capture does not register.
You will need to have installed the HypnOS DreamToolz app installed. If you don't have the Dreamtoolz, check out the guide here
Any time you see garbled nonsense text on screen, then you will need to reload it in safe mode. Just click the yellow ! triangle at the top left of the window near the ban hammer. You can click it a few times to make sure it registers.
Appart from the messed up text pages, there are other pages that require safemode, if you have a page that refuses to register on the HAP, it is worth giving safe mode a couple clicks.
Pages that are not registering on the HAPMany pages seemed to resist being captured and would not turn blue whatever I did. Some need the safemode trick detailed above, some just need reloading a few times.
Generally, using the PREV and NEXT buttons on the CAPTURES window repeatedly to reload the page did the trick. Once you can load it a couple times without the HAP icon in the bottom right spinning and saying it's achiving the page, then it means the page has registered correctly. Some pages seem to need time to fully load before they will register.
Freelands map pages were a regular culprit, as were the Shopping Maul game pages. A lot of pages that exist in only one time seemed to not register, like world news pages. Just try a combo of date toggling and hitting safe mode and they should soon register.
Once you have 100% archived, the thanks app will download, open it and have a look at the three pages written by the devs. For me the achievement popped after reading two pages and then opening the HAP.
Hope this helps and I didn't miss anything, I was pulling my hair out with this and it took much longer than it should have, hopefully I can save you the same headaches.