Yeah, I have Sierra on a separate SSD for testing until it's running perfect.Those graphic remnants in the upper left corner are unacceptable to me so I reverted back to El Capitan until the issue is resolved.
Go to your BIOS setting when you first turn your computer on by hitting the delete key while its preparing to boot. Look in System Agent in your settings for Video settings where you set it to IGPU and there should be a setting for Video Memory. That is where you can change it and if it's like my Asus BIOS it defaults to 32. Most people say to increase to at least 64 but I find that 128 works best for me.
Also, and I am far from an expert but you should mount your EFI partition when running Multibeast so it's actually changing the settings for the 530. You should use EFI Mounter v3 which is located in downloads and diskutil list command in terminal to make sure you have the correct partition mounted if you have more than 1.
I had that problem with El Capitan once and did a clean install to fix it. I would suggest to wait until Multibeast 9 which should be out anytime and try to fix it then. From what I hear there is a problem with Clover and they are waiting for a fix.Tried that, set it to 512MB (max value possible). But macOS still detects only 18MB, same as on the first image. Any idea of what else might I be missing?
I had that problem with El Capitan once and did a clean install to fix it. I would suggest to wait until Multibeast 9 which should be out anytime and try to fix it then. From what I hear there is a problem with Clover and they are waiting for a fix.