DIMM and PCI Card Guidelines

Can someone explain me the PCI-E slot variations & sizes of pci slot 1 SYONCON PCIe Multiplier, PCIe Splitter 1 to 4 PCI-Express 16X Slots Riser Card, PCI-E 1X to External 4 USB Adapter for BTC Miner Machine GPU Mining · 5 pcie gen 4 in gen 3 slot Card capacity and size Mac Pro has eight PCIe x16* sized slots that accept many different types of PCIe cards: Slot 1: up to x16

pcie training error slot 1 List of Motherboards with 1 PCI-Express x16 Slots: ASRock B760M-H, ASRock H610MAC, ASRock B760M-HDV, ASRock H610M-HDV+ D5, GIGABYTE B650M D3HP,