A Realtek Ethernet Controller was on my old PC and it is on my new MinisForum MC560 PC and it is on my old Lenovo laptop. My old PC had an Intel AX200 wireless interface; my old Lenovo laptop has a Realtek wireless interface; my new PC has a MEDIATEK wireless interface. So there seems to be nothing in common between the problem PCs (old PC & new PC) which the Lenovo laptop has, except that the problem PCs are AMD Ryzen processors and the Lenovo laptop is a Pentium 1 processor! 

My new PC doesn't even have WireGuard on it whereas my old PC had WireGuard on it, as I've decided to use a Raspberry Pi model 4 B for that. 

Here is network details for new PC:
john@Desktop:~$ sudo lshw -C network
  *-network                 
       description: Ethernet interface
       product: RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
       vendor: Realtek Semiconductor Co., Ltd.
       physical id: 0
       bus info: pci@0000:01:00.0
       logical name: eno1
       version: 15
       serial: 58:47:ca:70:a0:ea
       size: 100Mbit/s
       capacity: 1Gbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=5.19.0-45-generic duplex=full firmware=rtl8168h-2_0.0.2 02/26/15 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
       resources: irq:24 ioport:f000(size=256) memory:fcf04000-fcf04fff memory:fcf00000-fcf03fff
  *-network
       description: Wireless interface
       product: MEDIATEK Corp.
       vendor: MEDIATEK Corp.
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: wlp2s0
       version: 00
       serial: 10:6f:d9:cf:d1:69
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=mt7921e driverversion=5.19.0-45-generic firmware=____010000-20220209150915 ip=192.168.1.110 latency=0 link=yes multicast=yes wireless=IEEE 802.11
       resources: irq:67 memory:e0300000-e03fffff memory:e0400000-e0403fff memory:e0404000-e0404fff

john@Desktop:~$ ifconfig
eno1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        ether 58:47:ca:70:a0:ea  txqueuelen 1000  (Ethernet)
        RX packets 79903  bytes 6374933 (6.3 MB)
        RX errors 0  dropped 35  overruns 0  frame 0
        TX packets 3769  bytes 871473 (871.4 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 28449  bytes 3223428 (3.2 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 28449  bytes 3223428 (3.2 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlp2s0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.110  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::d63e:3edb:8f82:6f7f  prefixlen 64  scopeid 0x20<link>
        ether 10:6f:d9:cf:d1:69  txqueuelen 1000  (Ethernet)
        RX packets 2172914  bytes 1928088175 (1.9 GB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 666334  bytes 168574947 (168.5 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0