Again, a major change in a LTS release…
I’m disappointed you dropped the mini.iso with debian installer. It was worked fine until focal RC. Why did you drop it just before final release? I repeat, it was worked fine with RC release!
Your new method force to download 900mb of file just to boot the installer. This is very bad.
I also have issue to use my local mirror with custom apt keys. I just can’t start the install, the installer just crash with cryptic error. The documentation is very basic too.
I hope you change idea and release a new debian-installer compatible with final release.
Thanks!