Question: it used to be possible to access an FAT 32 Ubuntu (18.04) formatted flash drive in my Win 10 PC.
For some time now, When I plug an Ubuntu formatted USB drive (tried 3 different ones) it is not recognized and the Bluetooth keyboard mouse freezes.
Removing the flash drive situation becomes normal. Tried all the ports.
The Flash drive and the Bluetooth one are in different ports, but it doesn't matter.
I use Nautilus, no option offered.Tried also with Disks and Gparted.

Purchased a brand new Sandisk drive. Here's how it went: Just plug it to the PC - OK. Format in Ubuntu as above, First pug in not recognised by PC, remove and replug Kaspersky message external device should be scanned, scan was clean, drive is recognized. This is repetitive. Mouse and keyboard working normally.

Thanks, tried your CL. All I get is error "Device partition expected, not making filesystem on entire device '/dev/sdc' (use -I to override)"
(drive is 16GB)

Answer: 
Wireguard is started via `systemd-networkd`. The installation also creates a new interface `wg0`.

The configuration is done via two files (`somename` can be anything, for instance `wg0` or `wireguard`)(1)

1. `/etc/systemd/network/somename.netdev`

This file will hold the configuration of the [interface](https://www.freedesktop.org/software/systemd/man/systemd.netdev.html#%5BWireGuard%5D%20Section%20Options) and [peers](https://www.freedesktop.org/software/systemd/man/systemd.netdev.html#%5BWireGuardPeer%5D%20Section%20Options). It uses `[WireGuard]` and `[WireGuardPeer]` instead of the usual `[Interface]` and `[Peer]` (see (1))

```
[NetDev]
Name = wg0
Kind = wireguard
Description = Wireguard

[WireGuard]
ListenPort = 51820
PrivateKey = <your private key>

# laptop
[WireGuardPeer]
PublicKey = h/trC+5Z8qbGBJtroYITQGMNUn5XQZ/JRqVR3iIH5Ro=
AllowedIPs = 192.168.20.2/32

```

2. `/etc/systemd/network/somename.network`

This file will hold the IP-related configuration of the interface (nothing specifically wireguard-related here)

```
[Match]
Name = wg0

[Network]
Address = 192.168.20.1/32

[Route]
Gateway = 192.168.20.1
Destination = 192.168.20.0/24

```

These configuration files are read upon a `systemctl [re]start systemd-networkd`.

---

(1) Note that the configuration file referred to in various documentations (`/etc/wireguard/wg0`) is not used with `systemd-networkd`. It would be used if you ran `wg-quick` commands.

*This answer is here thanks to [@Rinzwind](https://askubuntu.com/users/15811/rinzwind) and him pointing to `systemd-networkd` and its configuration files*
I am adding another answer because I ended up using another approach. That one is based on the `wg-quick@.service` template.

I enable (and start, stop, etc.) it via `systemctl enable wg-quick@wg0.service` and the configuration lives in `/etc/wireguard`. It has the classical format of Wireguard.

In order to manage the configuration, I use the excellent [Wg Gen Web](https://github.com/vx3r/wg-gen-web) interface.