I haven’t used nextcloud, but having /var on an actual disk might help, if nextcloud writes to it often. Even if it doesn’t, it might still help a bit as a lot of software does, so it will still reduce the writes to the SD card.
You don’t actually need much on your root partition. Only /etc, /bin, /lib & if it’s separate, /sbin. Most distributions (inc. recent Debians, not sure which version rpi os uses) have symlinked /bin, /sbin & /lib with their /usr counterparts. This means that the binaries & libraries actually reside under /usr, so it has to be on the root partition, but /usr/local should be safe to move.
This means that you can put all the absolutely required directories on the SD card and everything else on a real drive.
It doesn’t say anything about performance. But they now support Vulkan with Nouveau, so it can now be used even if OpenGL is not available or broken.
The blog post only me tioned that the driver now supports the GPUs, which I think should be believable, as the GPUs are listed as conformant on Khronos’ website.
If you have had problems with a Wayland compositor when using Nouveau with one of the cards, it is possible that it might work now, if the compositor supports Vulkan.
Vulkan is normally faster than OpenGL, but I don’t know much about the state of NVK & Nouveau’s OpenGL driver for the cards. I just know the API versions they support and that NVK cannot reclock them if Nouveau can’t, so I can’t say anything about performance.