Exchange 2016 CU23 SU9v2 installed without errors, all services came back online like they are supposed to do.

MS rereleased the update, supposedly it is fixed now. We will look out for other reviews before installing.
https://techcommunity.microsoft.com/t5/exchange-team-blog/re-release-of-august-2023-exchange-server-security-update/ba-p/3900025

The Exchange Server SU breaks non-English Servers. MS acknowledged the issue and provides an official workaround.
https://support.microsoft.com/en-us/topic/exchange-server-2019-and-2016-august-2023-security-update-installation-fails-on-non-english-operating-systems-ef38d805-f645-4511-8cc5-cf967e5d5c75

never done p2v but v2v before, using the starwind converter. it’s a freeware and I just read it can also do p2v. proxmox itself is not available as a target, so you might have to convert your server to an esxi-vm, and then again from there to proxmox 🤔 that might be the slowest and one of the dirtiest ways to tackle this, but it might work

here’s the link to the converter software: https://www.starwindsoftware.com/starwind-v2v-converter