Before you started the install, your EFI partition only had 3.2M free. Conservatively, you should budget 300M per kernel you install. It could be a lot less than that depending on what drivers you need though.
Thanks for the really quick answers!
I found the reason for the error:
My EFI partition is 500MB in size, so I assumed this should be okay. But I found out only 100MB of it was formatted.
I formatted the partition, now it’s 500M and the installation worked without issues.
I have to install the Windows boot loader again though. visible pain