It looks like it is one, but dmidecode doesn’t show it.

# sudo dmidecode --type slot           
# dmidecode 3.4
Getting SMBIOS data from sysfs.
SMBIOS 3.0.0 present.

Handle 0x001C, DMI type 9, 17 bytes
System Slot Information
        Designation: J6B2
        Type: x16 PCI Express
        Current Usage: Available
        Length: Long
        ID: 1
        Characteristics:
                3.3 V is provided
                Opening is shared
                PME signal is supported
        Bus Address: 0000:ff:10.0

Handle 0x001D, DMI type 9, 17 bytes
System Slot Information
        Designation: J6B1
        Type: x1 PCI Express
        Current Usage: Available
        Length: Short
        ID: 2
        Characteristics:
                3.3 V is provided
                Opening is shared
                PME signal is supported
        Bus Address: 0000:ff:1c.4

Handle 0x001E, DMI type 9, 17 bytes
System Slot Information
        Designation: J6D1
        Type: x4 PCI Express
        Current Usage: Available
        Length: Long
        ID: 3
        Characteristics:
                3.3 V is provided
                Opening is shared
                PME signal is supported
        Bus Address: 0000:ff:1d.0

Handle 0x001F, DMI type 9, 17 bytes
System Slot Information
        Designation: J7B1
        Type: x1 PCI Express
        Current Usage: Available
        Length: Short
        ID: 4
        Characteristics:
                3.3 V is provided
                Opening is shared
                PME signal is supported
        Bus Address: 0000:ff:1c.5


Wrong DMI structures length: 3135 bytes announced, structures occupy 3136 bytes.