yes, it is 
Then you can’t load vfio at boot as you will lose access to the host … You need to follow a different tutorial specific to having only one GPU …
Wiki · Risingprism / Single GPU Passthrough · GitLab)-Preparations
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Oh damn! I see, will look into this in that case 
In case I can, is there a cheap GPU you recommend for a host, to keep the good one in the VM?
Good catch!
I, personally, use AMD Radeon RX550s for that purpose. But you might want to make sure your B550 board has the IOMMU groups set up correctly. They are not know to have great groupings. I want to avoid that you buy a second GPU just to find them both in the same IOMMU group.
user ~ $ for d in /sys/kernel/iommu_groups/*/devices/*; do n=${d#*/iommu_groups/*}; n=${n%%/*}; printf 'IOMMU Group %s ' "$n"; lspci -nns "${d##*/}"; done;
IOMMU Group 0 00:01.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 0 00:01.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse GPP Bridge [1022:1483]
IOMMU Group 0 00:01.2 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse GPP Bridge [1022:1483]
IOMMU Group 0 01:00.0 Non-Volatile memory controller [0108]: Phison Electronics Corporation E12 NVMe Controller [1987:5012] (rev 01)
IOMMU Group 0 02:00.0 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] Device [1022:43ee]
IOMMU Group 0 02:00.1 SATA controller [0106]: Advanced Micro Devices, Inc. [AMD] Device [1022:43eb]
IOMMU Group 0 02:00.2 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Device [1022:43e9]
IOMMU Group 0 03:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Device [1022:43ea]
IOMMU Group 0 03:06.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Device [1022:43ea]
IOMMU Group 0 03:07.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Device [1022:43ea]
IOMMU Group 0 03:08.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Device [1022:43ea]
IOMMU Group 0 03:09.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Device [1022:43ea]
IOMMU Group 0 07:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 15)
IOMMU Group 0 08:00.0 Network controller [0280]: Intel Corporation Dual Band Wireless-AC 3168NGW [Stone Peak] [8086:24fb] (rev 10)
IOMMU Group 10 00:18.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 0 [1022:1440]
IOMMU Group 10 00:18.1 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 1 [1022:1441]
IOMMU Group 10 00:18.2 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 2 [1022:1442]
IOMMU Group 10 00:18.3 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 3 [1022:1443]
IOMMU Group 10 00:18.4 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 4 [1022:1444]
IOMMU Group 10 00:18.5 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 5 [1022:1445]
IOMMU Group 10 00:18.6 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 6 [1022:1446]
IOMMU Group 10 00:18.7 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Matisse/Vermeer Data Fabric: Device 18h; Function 7 [1022:1447]
IOMMU Group 11 0c:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Function [1022:148a]
IOMMU Group 12 0d:00.0 Non-Essential Instrumentation [1300]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse Reserved SPP [1022:1485]
IOMMU Group 13 0d:00.1 Encryption controller [1080]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse Cryptographic Coprocessor PSPCPP [1022:1486]
IOMMU Group 14 0d:00.3 USB controller [0c03]: Advanced Micro Devices, Inc. [AMD] Matisse USB 3.0 Host Controller [1022:149c]
IOMMU Group 15 0d:00.4 Audio device [0403]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse HD Audio Controller [1022:1487]
IOMMU Group 1 00:02.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 2 00:03.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 2 00:03.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse GPP Bridge [1022:1483]
IOMMU Group 2 09:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 10 XL Upstream Port of PCI Express Switch [1002:1478] (rev c1)
IOMMU Group 2 0a:00.0 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 10 XL Downstream Port of PCI Express Switch [1002:1479]
IOMMU Group 2 0b:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 22 [Radeon RX 6700/6700 XT / 6800M] [1002:73df] (rev c1)
IOMMU Group 2 0b:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Navi 21 HDMI Audio [Radeon RX 6800/6800 XT / 6900 XT] [1002:ab28]
IOMMU Group 3 00:04.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 4 00:05.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 5 00:07.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 6 00:07.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse Internal PCIe GPP Bridge 0 to bus[E:B] [1022:1484]
IOMMU Group 7 00:08.0 Host bridge [0600]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse PCIe Dummy Host Bridge [1022:1482]
IOMMU Group 8 00:08.1 PCI bridge [0604]: Advanced Micro Devices, Inc. [AMD] Starship/Matisse Internal PCIe GPP Bridge 0 to bus[E:B] [1022:1484]
IOMMU Group 9 00:14.0 SMBus [0c05]: Advanced Micro Devices, Inc. [AMD] FCH SMBus Controller [1022:790b] (rev 61)
IOMMU Group 9 00:14.3 ISA bridge [0601]: Advanced Micro Devices, Inc. [AMD] FCH LPC Bridge [1022:790e] (rev 51)
Does this look good? I’m sorry, I’ve never done this before, so I have very little experience and can’t seem to find good information on it on my own. 
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This does not tell me much. What you would need to do is, you need to plug a PCIe device in the slot where the second GPU would go and look in which group it ends up. If it ends up in the same group as other devices it becomes more complicated. This would mean for example that your only chance to fix it, is to compile the kernel yourself with the ACS override patch. However if it ends up in its own group you should be ready to go.