TYPO3 Core

Yes, base in site config is:

https://mydomain.com/

to make reproducing a bit easier, which code do you use to generate the URL?

This is the code we use:
[[https://github.com/aimeos/ai-typo3/blob/master/lib/custom/src/MW/View/Helper/Url/Typo3.php#L80-L88]]

Has the behavior changed in 10.4.17 if the parameter for setAbsoluteUriScheme() is empty?

Problem solved by removing setAbsoluteUriScheme()!

I traced it back to #90228.

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/71997

Patch set 1 for branch 10.4 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/71927