Spent two whole hours last night trying to get MinUI onto the device but failed spectacularly. I'll briefly describe the troubles I went through.
MinUI readme says that the stock SD card it comes with is overly exaggerated as being bad, it says that it is good to install the OS on, then use slot 2 with a better SD card to hold the emulators and game files. I flashed the stock SD card using Raspberry Pi Imager, which worked when installing MuOS, but somehow formatted the card in a way Windows couldn't read.
I jumped to Copilot for help. Copilot walked me through some cmd prompts to try, and when that wasn't working, it suggested me to try the official SD Association imager software. I downloaded that, ran it, just to find out it doesn't support formatting SD cards that are above 32GB to fat32. What the hell... so then Copilot suggested another program, GUI Imager or something like that, which worked like a complete charm.
From there, I then found out that MinUI requires to be installed OVER the stock Anbernic OS... after I had went through all this trouble of flashing the card. So, I redownloaded a copy of it, used Rufus to create it into a bootable drive, made sure it worked, then proceeded to try to install MinUI.
I followed the steps in the readme closely. I thought I did everything right. Certain files go into the stock SD card, the rest goes into the second card. Nothing. It didn't turn on. I should have followed a video tutorial, but at that point it was almost two hours of me messing with it. I was done. I reinstalled MuOS which takes no effort at all and got it up and running again.
I did look into Knulli, but I don't like how I can't drag and drop files from Windows directly on the SD card. Everything I read said it requires third party programs to put files onto it... no thank you. I much prefer to just pop the card into my PC and manage it from there, no extra software required. I'm not 100% sure if that is the case, but at least one tutorial I read on it said it requires some different software to manage it via Windows.