I signed up to also report I updated to 8.2 and AMD 6600XT passthrough broke and I couldn't fix!
I've rolled back to 8.1 (
https://enterprise.proxmox.com/iso/), haven't done passthrough just yet, still reading up and researching.  But my system was running fine until I updated.
Intel 14th Gen i5 CPU & MSI Z790 Edge TI MoBo.
		
 
		
	 
Ill setup a testing rig (I'm on 7002 Epyc and a Zen3 5800X3d with a 6600X) by next weekend. But since you seem to be able to test this, do you mind rolling kernel 6.6 and 6.7 and seeing if the IOMMU/VFIO passthrough is working? I think Linux updated for IOMMU SVA starting with 6.8, which could be why its failing on that kernel for AMD systems. There is a patch on 6.8.7 addressing SVA for some of the Qualcomm SOCs, so this could be entirely related since IOMMU SVA is a faily new feature. 
6.7 patch to address IOMMU SVA issues on 6.6 - 
https://lore.kernel.org/lkml/ZUkXojmVf2CmkXHh@8bytes.org/
Phoronix's coverage on this a bit - 
https://www.phoronix.com/news/AMD-IOMMU-SVA-Nears
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IOMMU Updates for Linux v6.7
Including:
    - Core changes:
      - Make default-domains mandatory for all IOMMU drivers
      - Remove group refcounting
      - Add generic_single_device_group() helper and consolidate
        drivers
      - Cleanup map/unmap ops
      - Scaling improvements for the IOVA rcache depot
      - Convert dart & iommufd to the new domain_alloc_paging()
    - ARM-SMMU:
      - Device-tree binding update:
        - Add qcom,sm7150-smmu-v2 for Adreno on SM7150 SoC
      - SMMUv2:
        - Support for Qualcomm SDM670 (MDSS) and SM7150 SoCs
      - SMMUv3:
        - Large refactoring of the context descriptor code to
          move the CD table into the master, paving the way
          for '->set_dev_pasid()' support on non-SVA domains
      - Minor cleanups to the SVA code
    - Intel VT-d:
      - Enable debugfs to dump domain attached to a pasid
      - Remove an unnecessary inline function.
    - AMD IOMMU:
      - Initial patches for SVA support (not complete yet)
    - S390 IOMMU:
      - DMA-API conversion and optimized IOTLB flushing
    - Some smaller fixes and improvements