I ran through an unattended installation on Debian 10 yesterday (1/28/2020), and it worked flawlessly for me out of the box. I didn't have to adjust anything for Apache2. What version of Apache2 are you running? Also, where can I obtain the Debian 10 image that Proxmox uses so that I can test this further? If you're having this strange issue, it's probably a result of the installer not doing something correctly.
Please let me know.