There are already some threads on the topic. None directly targeted towards Debian Bookworm. All tinkering with repositories and dependencies.
While searching for information I came hence to the conclusion, there should be a more straightforward way. I'd herewith like to point out what can be done to get Dell iDrac Linux tools set up. That is racadm and iSM - the user space iDrac Admin tool and the service providers for BS menu entries in iDrac web interface.

This is not intended to be a step by step howto. So let's fast forward to necessary steps and hints.
Also please take note there is not only forum threads here but some blogs, too, e.g. williamdes or privex.

racadm

• find Dell iDRAC Tools for Linux in a recent version. I used v11.3.0.0 like so: Dell driver download
• download to some location and un-tar
• find UBUNTU22 folder in the hierarchy and 3 deb archives inside
  • srvadmin-hapi_11.3.0.0_amd64.deb
  • srvadmin-idracadm7_11.3.0.0_all.deb
  • srvadmin-idracadm8_11.3.0.0_amd64.deb
• install libcrypto++8and build-essential
• use dpkg --install and install all 3 deb archives which should just work on a Bookworm system
• if you want create a symlink to the binary ln -s /opt/dell/srvadmin/bin/idracadm7 /usr/local/bin/racadm
• test with racadm getsysinfo

iSM

• find and download iSM packages which support your server / idrac generation. For me it is 13th gen right now. Hence I resort to iSM/5300/bullseye/pool/main/dhere: dcism
• you will need both, dcism and dcism-osc - again 2 deb archives - download to some location of your choice
• you will need a openssl 1.1.1 version, too
• fetch source openssl-1.1.1o
• un-tar, ./config && make && make test && make install and run ldconfig -v
• be aware: in a production system you wouldn't want an openssl 1.1.1 version to be globally linkable in the system, but if this was a production system you would not use 13th gen or likely have professional Dell support anyways
• now install both deb archives and validate the dcism service starts correctly (which will be depending on a supported openssl 1.1.1 version)
• enable and see data popping up in iDrac web interface timely

Overall not much tinkering, just some archive download, no repository experiments and scripting or pinning of old versions.
Works in my lab environment. YMMV

Let me know if these hints were of any help. I appreciate it.

Best, Markus

Thank you @complexplaster27 for this update. It does in fact work to update to dcism-osc_8.1 - you definitely then want to make sure a compatible dcism version is installed, too, like 6.1 mentioned in your post.
Keep in mind though, you wouldn't normally want to mix Debian and Ubuntu repositories and packages. But not to worry, the Debian version can be installed. Which would be: dcism_6.1.0.0-4104.debian11_amd64.deb

I found out extremely quickly why the Ubuntu24 package is not the right way:

See: https://github.com/satorisage/dell-ism-proxmox-9.1-patch (good explanation why it happens but I don't trust running a random github script with no vetting)

I had this issue where 2min 58ms systemd-udev-settle.service I thought it was the Broadcom NIC taking ages to start trying to following this thread: https://forum.proxmox.com/threads/broadcom-nics-down-after-pve-8-2-kernel-6-8.146185/

I removed both dcism and dcism-osc and restarted the Proxmox it booted up very fast.