Per Google the Dell 0NC2VH is an Intel Q370 chipset motherboard used in the Optiplex 7060. Dell motherboards are proprietary and do not follow ATX standards, some Google images depict the board with a blue x16 PCIe slot and some do not. You will need to verify whether your board has that or not.
Also the Q370 only supports PCIe gen 3.0 and the RX 6400 is a PCIe gen 4.0 card. It should work in an older gen PCIe slot however available bandwidth will be halved. This shouldn't be a problem if you're only using it for display purposes and you're not gaming on it.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT
Ryzen R7 5700G | B550 Gaming X | 2x8GB G.Skill 4000 | Radeon Vega 8 IGP
Ryzen R5 5600 | B550 Gaming Edge | 4x8GB G.Skill 3600 | Radeon RX 6800XT