@Deuterium Oxide
AndrewT suggested I post my (now resolved) issues with the launcher here.
I was unable to play any games that required the new launcher (Prison Architect and Stellaris). The first issue was that the game was unable to locate the "launcherlocation" file in "\paradoxinteractive\launcherlocation". A quick search indicated the file was in "C:\paradoxinteractive" instead. The computer's registry also said it was in "C:\paradoxinteractive"
I copied this file across to where the game thought it should be and received a long string of javascript errors (see attached image).
I tried a few different things. Full uninstall of both Prison Architect and Stellaris (including deleting every mention of them in my registry as well as save data). Full uninstall of the launcher. Uninstalled Java, restarted, reinstalled java, restarted, reinstalled Prison Architect (it's smaller). Exact same errors. Tried downloading the launcher from the website, still crashed. Launching it from where it was installed, still crashed.
Finally tried it on my wife's computer, it worked. Went as far as copying the installations of both the launcher and the game from her computer to mine, changing registry files to match up, still didn't work.
The only difference was my computer's somewhat unique layout. I have an SSD for windows and a few programs I want to run quickly. I was running out of space on this SSD (even after moving a lot of things off it) and so the only other thing I could feasibly move became game data which was stored in appdata/local. I changed the location of appdata/local from "C:\Users\[username]\appdata\local" to: "C:\Storm(this is a different hard drive)\[username]\appdata\local". This has only ever been a problem for google chrome and one or two other programs, and as it happens.. the Paradox Launcher.
Once I changed the appdata/local location back to its default and uninstalled the launcher, the game worked fine. I checked the registry and it had put its launcherlocation file in the right place and the game was actually paying attention to the registry as well.
Note: It's not like "users\[username]\appdata\local" didn't exist. This was the problem with chrome, despite me moving where it was supposed to be, chrome ignored this and just stored all its data there anyway. The paradox launcher did NOT do this, it stored everything in "storm\username\appdata\local" like it's supposed to, and then had a heart attack. After I changed the location of appdata back to default, the launcher was still located in "storm\username\appdata\local\programs\paradox interactive" and it recognised this and was fine with it (I've since changed this so it's not confusing me).
Also:
https://support.paradoxplaza.com/hc/en-us/articles/115003166953-Paradox-Launcher-FAQ does not report Prison Architect as being a game that currently uses the paradox launcher, as well as a couple others. This was a touch problematic since I was trying to do all this reinstalling stuff on Stellaris which is a notably larger game, unaware that Prison Architect (which was also installed) also used the launcher. I only found out because I downloaded the version from the website and found a list of assets for various games it supported.
Sorry for the long post, I just like to be thorough.