A few days ago I did a Debian install with the firmware-testing-amd64-netinst.iso I believe I downloaded on June 5, 2021. I figured it was close enough to bullseye becoming the stable release that the testing image would be quite stable enough and not likely to change too much, so I could just set the repositories to bullseye and let the installation mature to stable.
I was shocked with the installer didn't recognize my ethernet card and set up DHCP. Nor did it recognize my wireless adapter. They are pretty bog-standard, Gig RTL8111/8168/8411 + Broadcom Wifi. The installer gave me an option to insert a USB stick with the proper firmware. What the heck is to point of downloading the firmware version of the installer if I have to download the firmware separately?
So I just did the basic stripped-down install figuring I'd just 'dpkg -i' the firmware packages later and 'tasksel' myself to a regluar desktop. Before I got around to it I read on Phoronix that the Debian 11 "Bullseye" installer RC2, so I downloaded and flashed debian-live-blsy-DI-rc2-amd64-kde+nonfree.iso and booted my system from it, and guess what? On a 3.2 GB ISO the firmware also didn't load, I couldn't get an internet connection. The firmware is on the ISO, but it isn't automatically activated, you have to do some CLI-fu to get your internet connection to work, not user-friendly! A cursory glance showed there were plenty of activated international fonts and locales, but the firmware was not apparently installed.
I ended up rebooting to the minimal installed system and installing the firmware deb files from a USB stick. This sort of behavior should be a release blocker.
By the way, I installed from the debian-live-amd64-kde+nonfree.iso a few years ago, I don't remember if it was jessie or one of the later releases. It installed a metric ton of extra localizations and fonts that made the system very slow to update, I had to manually hunt down those packages and remove them. I just don't use Esperanto or Xhosa on a regular basis. If this is still the case with these firmware ISOs I would recommend that you revisit that policy.