These are the steps I used to add two cursors on Ubuntu 24.04 (I used the documentation from Arch Linux web site, see below)

Add an “Auxiliary” pointer/keyboard to your xinput:

$ sudo xinput create-master "Auxiliary"

Run “xinput list” and you will see something like this at the end:

⎡ Auxiliary pointer                   	id=17	[master pointer  (18)]
⎜   ↳ Auxiliary XTEST pointer             	id=19	[slave  pointer  (17)]
⎣ Auxiliary keyboard                  	id=18	[master keyboard (17)]
    ↳ Auxiliary XTEST keyboard            	id=20	[slave  keyboard (18)]

Now plug your external mouse and run “xinput list” again, you will see that a new device appeared in your list, example:

⎡ Virtual core pointer                    	id=2	[master pointer  (3)]
⎜ ...
⎜   ↳ Logitech M510                           	id=21	[slave  pointer  (2)]
⎣ Virtual core keyboard                   	id=3	[master keyboard (2)]

Now re-attach this device to your auxiliary pointer:

$ sudo xinput reattach 21 "Auxiliary"

You will see that a new mouse appeared in your screen and you can move it independently of you initial mouse cursors.

Source: https://wiki.archlinux.org/title/Multi-pointer_X#:~:text=When%20an%20application%20grabs%20input%20(e.g.%20a,a%20different%20one%20with%20a%20%22xinput%22%20utility.