Multiple-monitor Set Up Makes Mouse-pointer Jump About in 20.04

I have recently loaded Ubuntu 20.04 to dual-boot on a Packard Bell with Windows 10 Home 64-bit already installed. The mouse-pointer moves and clicks perfectly when the PC has a single-monitor. However, for work as a developer, I should like to use a dual-monitor setup.

The problem I have is, if I plug in to the PC tower a second monitor and follow the steps to Connect Another Monitor To My Computer (https://help.ubuntu.com/stable/ubuntu-help/display-dual-monitors.html), and after I confirm "join Display", the mouse-pointer jumps about and a second stationary mouse-pointer appears in the bottom right of my primary screen. This behaviour stops immediately I confirm "Single Display", but now the second screen is now turned blank.

$ xinput
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ USB Wired Keyboard Consumer Control id=12 [slave pointer (2)]
⎜ ↳ PixArt USB Optical Mouse id=13 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
    ↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
    ↳ Power Button id=6 [slave keyboard (3)]
    ↳ Video Bus id=7 [slave keyboard (3)]
    ↳ Power Button id=8 [slave keyboard (3)]
    ↳ Sleep Button id=9 [slave keyboard (3)]
    ↳ USB Wired Keyboard id=10 [slave keyboard (3)]
    ↳ USB Wired Keyboard System Control id=11 [slave keyboard (3)]
    ↳ USB Wired Keyboard Consumer Control id=14 [slave keyboard (3)]

$ sudo dmidecode -t 1
# dmidecode 3.2
Getting SMBIOS data from sysfs.
SMBIOS 2.8 present.

Handle 0x0001, DMI type 1, 27 bytes
System Information
    Manufacturer: Packard Bell
    Product Name: iMedia S2984
    Version:
    Serial Number: DTU96EK00360103D0F3000
    UUID: 84edd4a2-b457-11e5-9b1f-98eecb2ca5dd
    Wake-up Type: Power Switch
    SKU Number:
    Family: Packard Bell Desktop

$ lsb_release -a; uname -a; lsusb
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04 LTS
Release: 20.04
Codename: focal
Linux charlesb2t-iMedia-S2984 5.4.0-37-generic #41-Ubuntu SMP Wed Jun 3 18:57:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 004: ID 0bda:0153 Realtek Semiconductor Corp. 3-in-1 (SD/SDHC/SDXC) Card Reader
Bus 001 Device 003: ID 093a:2510 Pixart Imaging, Inc. Optical Mouse
Bus 001 Device 002: ID 0461:4e6f Primax Electronics, Ltd Acer Wired Keyboard Model KBAY211
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Should I report this as a bug, or is there something I can do?

Any help will be appreciated. Otherwise, to carry on my work it looks as though I need to go back to Windows 10 :-(