I cannot install drupal 11 on a fresh Debian install, in fact I tried everything and it's no more the fault of proxmox, but the PHP installation.
Drupal 11 needs php 8.3 to work, but Debian official repos go only to php 8.2, so I used the sury.org Debian repo to install the latest PHP version. And this is the start of the problem, this install gives me the error shown in the other post, exhausted memory.
I search in the info.php, memory related stuff, and the only difference between the "official" PHP (8.2) and sury one is that in the mysqldn section it shows statistics to yes. But I don't know how to disable it...
I wanted to recommend using a Docker container but I ran into the same issue with the default config for "drupal:10-apache" (aka "drupal:10.3.7-apache-bookworm"). Opening "node/add/article" results in the OOM error. Downgrading to "drupal:10.3.6-apache-bookworm" resolved the issue. Looks like a Drupal regression to me. Maybe you can also try an older version of Drupal 11?
In fact when using PHP from sury.org the PHP 8.3 is available in addition to PHP 8.2. When using the phpinfo() and comparing the two PHP versions the only difference related a bit to memory are the statistics that are turned on. Nothing really more
This is why I made a new thread because the error is not coming from anything else than the php repo of sury.org, no more a "self-hosted" or Linux proxmox issue.
EDIT : tried the same install in KVM and on my desktop, it's not working. Tried Debian 10 with official PHP and it's working