Is it possible to avoid expensive TRX50 and remain on cheaper AM5 design with single motherboard supporting simultaneous use of both one modern GPU (6000 series or better) and one x4x4x4x4 Pcie 4.0/5.0 expansion pcie card?
Usage: Very seldomly for gaming mostly other Proxmox related homelab activities.
It seems the answer is no, but I wanted to confirm, before abandoning AM5 idea.
If you are willing to run your GPU in an x4 setup then yes, a few models.
Otherwise, no. At most one x8 and one x4/x4. 
If you have a PCIe Gen3 dGPU you have exactly one AM4 motherboard model (ASUS Pro WS X570-ACE) that generates 8 PCIe lanes from the X570 chipset to the chipset PCIe slot.
If you use a Gen4 dGPU this doesn’t matter any more since then the bottleneck is shifted to the CPU-Chipset interface which is PCIe Gen4 x4, and this unfortunately hasn’t changed with AM5, yet. Maybe with X770 in 2025, but there are no new AMD chipsets expected for 2024 that could increase the CPU-Chipset interface to PCIe Gen5 x4.
That’s the main reason I haven’t practically looked into AM5 yet, that and 64 GB ECC UDIMMs not yet being available make it feel more like a platform sidegrade.
Yeah, I’ve looked around for some offering on AM5 like this too, I can only find support for bifurcation on the first x16 slot
I wonder if there are any PCIe cards that have a proper PLX bridge to facilitate this ?
AM5 simply doesn’t have enough lanes to do 16 to the GPU and 16 more to nvme storage drives. Neither does mainstream Intel platform. In the past you either had to get a very expensive MB that has a PCIe multiplier/switch on the board or get a platform with more lanes them if you wanted to do that many high end parts in the PC. Now days I dont think there are any MBs with PCIe multipliers on them since the main company who made them (PLX) was bought up (by Broadcom) and the prices increased to astronomical levels that prevent them from being put in anything but a very expensive server board or special purpose hardware, and I dont think they even continued the line anymore. So your only solution is a higher end platform than mainstream. There are a couple newer companies that are recently making smaller PCIe switches though now, maybe someday we will again see them on mainstream boards again. Though that may be less likely with AMD and Intel adding 4 more lanes every 2-3 generations. It might not actually be needed anymore a few years down the line.
edit: the MSI MEG Z790 GODLIKE MAX WIFI is really expensive ($1100) but it does actually let you have 8 lanes for a GPU and still run 7 nvme drives, two of which are at PCIe 5.0 speeds.
Yes, they cost around $450-550 for the ones that have the PCIe chip on it to multiply the lanes and not need bifurcation. Compared to the $50-100 price of cards that just use bifurcation instead
Gigabyte B650 Aorus Master has 4 of M.2 Gen5 x4 straight off the CPU and leaves you an additional x8 Gen5 (CPU) for the GPU. Plus on top of that, Gen4 x4 + x2 through the chipset.
Nice, just checked it out and yes I see that model.
This could be a nice alternative to using a PCIe expansion card.