Hi ernstritoper,
Microsoft does not make Windows 10 or 11 DVD's they only supply Windows 10 and 11 on a USB flash drive, so if you are having problems after installing Windows from a DVD, so the DVD's may be corrupt, whoever created the DVD did not do a good job.
Yes, you are correct, the Windows installation files will fit onto a dual layer 8.5GB DVD, but not onto a standard DVD, which has a writable area of 4.35GB and the problem is usually whoever creates those DVD's overburns a 4.7Gb DVD
If you need to re-install Windows, then please create your own bootable USB and use that to clean install Windows.