Hello.
I am using the Asus TUF B450M-PLUS GAMING motherboard with the latest BIOS version 3802 together with an AMD Ryzen 5 5600.
Up to BIOS version 1804, PCIe 4.0 was supported for the PCIe x16 slot and the M.2 slot. After that, AMD blocked this function for this and other mainboards with the B450 and X470.
Is there already a BIOS MOD that unlocks PCIe 4.0 for the current BIOS 3802? Or is there a way to create such a BIOS MOD?
From what I have read unfortunately the answer is You can’t. Better save & buy b550 motherboard or find a b450 without the current/latest bios.
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I could just flash the BIOS with version 1804, which should support PCIe 4.0.
But will the processor I use be properly supported?
Why does it not work to mod a current BIOS to do this?
No, your CPU requires bios 3211.
TUF B450M-PLUS GAMING｜Motherboards｜ASUS Global
EDIT: UBU cannot add or remove mcodes or any other modules, the tool is an updater for existing modules only.
Modern AMD boards are not easy to mess with, due to cpu mcodes being attached to the AMD AGESA firmware.
EDIT: @ westlake Thank you my friend for the update on this bios, regarding mcodes, i didnt even looked if it was possible, glad you could confirm it to the user.
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Ok I understand… 
EDIT: Is the TUF B450M-PLUS GAMING BIOS not compatible with UBU ([Tool Guide+News] "UEFI BIOS Updater" (UBU))?
In the simplest case, the microcode from the AMD Ryzen 5 5600 can then be integrated into the BIOS 1804. And by the way, you could then renew all the other upgradeable components.
Surprisingly, this is not always the case. For example, this BIOS does not have the microcodes in the classic AGESA section. Therefore, you can change them easily. Modded BIOS file.
I think you have misunderstood something. In the 1814 BIOS, the PCIe 4.0 support for the 3000 series (Zen 2) was removed. This has nothing to do with the 5000 series (Zen 4). What is the original problem you posted about?
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Is there a guide how this works with the mainboard? Or should I stick to general existing guides for using UBU?
Edit:
Look here: Asus B450 and X470 Motherboards That Support PCIe 4.0 (Updated) | Tom's Hardware
AMD has caused the PCIe 4.0 support for this motherboard to be switched off again. 
Thank you for the BIOS MOD. But what kind of changes does this MOD contain?
I would very much like a BIOS MOD (BIOS 3802) with updated modules to all updateable firmwares + CPU microcodes + (if possible) PCIe 4.0 capability. 
Which are also supported by UBU.
EFI AMD RAIDXpert2-Fxx, EFI AMD GOP Driver, OROM VBIOS, EFI Realtek UNDI Driver, OROM Realtek Boot Agent GE, CPU Microcodes
I don’t think you can tamper with PCIe support because of AGESA, but if you have some documentation, I’d be happy to read it.
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Have I understood that correctly? The current BIOS MOD version 3802 of the TUF B450M-PLUS GAMING has been equipped with the new components that are currently available in UBU, namely the following:
- EFI AMD RAIDXpert2-Fxx
- EFI AMD GOP Driver
- OROM VBIOS
- EFI Realtek UNDI Driver
- OROM Realtek Boot Agent GE
- CPU Microcodes
The AGESA module cannot be replaced as a whole?
According to Asus, the AGESA module V2 PI 1.2.0.7 is currently in BIOS version 3802. If an exchange were somehow possible, you could create a second updated BIOS MOD (3802) with the AGESA module from BIOS version 1804 (Agesa 1.0.0.3 Patch AB).
If that is not possible, a completely updated BIOS 1804 with the latest versions of all firmwares and microcodes could be created.
EDIT: Unfortunately I don’t have any documentation on how to enable PCIe 4.0. You probably need to know where in the AGESA module this needs to be activated.
You great programmers and hackers of this time, have you still not found a way to replace the AGESA module in an UEFI BIOS? You can’t put up with something like that… 
Hello, is it also possible to create a modded BIOS with the latest BIOS of the MSI B450 Tomahawk Max that supports PCIe 4.0?