Today, I managed to get DSM 7.4 running on my RS3621xs+ using non-Synology drives, a process that required a lot of effort. To cut to the chase: there is absolutely no new function here that didn't already work in version 7.3!
After updating to 7.4, DSM no longer accepted my existing Volume 1. Since I don't own any genuine Synology drives, I had to add the drive to the internal database. In the end, however, I went ahead and performed a complete fresh installation with DSM 7.4.
As far as I'm concerned, DSM 7.4 is completely useless. Its only purpose is to force users into the Synology ecosystem. I would have at least expected my Nvidia GPU to be properly integrated for AI usage.
I will now follow the modern DSM approach and run DSM 7.x in Docker on ZFS. For this, I am using OMV7 on Debian 12 with the Proxmox kernel.