My guess is that the organizations that use Drupal in a purely Windows environment are in the government or education sectors. I say this because I work in the education sector that is nearly exclusively a Windows environment. We have a 70+ site multisite running in IIS.
Something I think that is overlooked in your stats above is sites that don't "phone home". After the issues with SolarWinds, our organization decided to prevent traffic like this on our servers. Updates are done on other computers via composer and uploaded to the web servers. I'm guessing that my organization isn't the only one that does something similar.
I realize that my organization is in the minority here, but it's only because the post in the sqlsrv driver Slack channel that I was even aware of this RFC. My personal opinion is that this RFC isn't allowing enough time for the affected organizations to find out about it in time to make comments on it. I believe this RFC should have come out when Drupal 10 was first started to be worked on if it was going to go away in Drupal 11.
I'd recommend allowing more time for comment by "advertising" it in all the Drupal 11 updates and then remove it in Drupal 12. This would allow organizations like mine more time to work on accommodations for this change.
Either way we'll figure it out. 3 weeks time to discuss this seems a bit too hasty.
My merge request may not be needed. It may just need that line removed. It appears that the next line in the code is effectively the same thing, but I haven't tested it.
After looking at the SimpleSamlPhp Slack, and then at the files in the download, it appears that this is an issue with extracting the files in Windows and it not creating the symlink for src/_autoload.php to lib/_autoload.php.
I hope this at least helps someone else in the future (most likely me). LOL
I think I found the root cause.
SimplesamlphpAuthManager.php::checkLibrary() loads the instance's /lib/_autoload.php. However, that file is blank.
This may mean that SimpleSamlPhp v2.1.1 is broken somewhere, but I haven't dug that far yet.
I can say that if you replace line 342 of SimplesamlphpAuthManager.php like below, everything seems to work properly in this module.
Old
include_once $dir . '/lib/_autoload.php';
New
include_once $dir . '/vendor/autoload.php';
When I submitted the changes to create a new column, migrate the data, then update the indexes, I did it with the idea that this is going to keep happening. Now, I am not 100% on my code changes working for every scenario, but it worked for me when updating to 9.3.x. Whatever is done here needs to work for any DB column changes. I'd be happy to help if given some direction on how the code I wrote for 9.3.x needs to be modified to get this working.