Stuck at grey screen with a white box and cursor | Vanilla Catalina i7-7700k RX580 H270M-ITX/ac

Sorry for the repost, my previous post got removed for using an anonfiles link.

I'm trying to install Catalina fresh onto my setup. I set up the installation USB via the Vanilla Hackintosh method suggested by this subreddit.

However, every time I boot I get stuck on this page:

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https://preview.redd.it/tffqbyzdsw341.jpg?width=1500&format=pjpg&auto=webp&s=55f06c67d7155ae67bc000a632eed9cf477c51aa

As you can see my cursor is on there; however, if I click on the white box then my cursor disappears permanently. It stays stuck on this screen indefinitely.

Before it goes into that state, this is what the verbose log output looks like:

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https://preview.redd.it/kqn1ymiesw341.png?width=3974&format=png&auto=webp&s=7344109a7eff4048cf445baa7cd7e199b8cf9077

Any ideas on why this would happen?

Things I have tried:

1. Rebuilding my installation USB - many times. I've tried with both the official Catalina installer and the Catalina Patcher too... no success either way.
2. Adding Lilu/WhateverGreen - done that. Doesn't work. InjectKexts is set to YES if you are wondering.
3. I am currently using the HDMI port on my dGPU, however I've also tried the DP port. The internal HDMI port doesn't give me anything.
4. I've tried using both iMac18,1 and iMac18,3 - no difference, same issue.
5. Booting into Windows. Windows recognises my RX580 just fine. Unigine Heaven scores are pretty normal too so I'm guessing that my graphics card is not the issue.

I can hear sound (the Mac "funk" sound when I press a key that's not allowed) so I'm guessing that it is a graphics issue.