An on-screen keyboard is showing up every time I touch a text field when I use an external monitor with touchscreen. I don't want/need this feature since I have a physical keyboard.

Here's a picture of the virtual keyboard:

I read a lot about this issue, but didn't find any solution. I tried the gnome-extension "Block Caribou" but it's not working. Also, the extension was only tested on gnome 3.26 according to gnome-extensions website, so not sure if it's working properly on my system.

Also, the on-screen keyboard is disabled in the accessibility settings (on the desktop and on the log-in screen). I think this keyboard must be located somewhere in my system and it should be possible to disable it if I would know where to look at.

System:
Ubuntu 20.04.4 LTS with Gnome 3.36.8

Any help or ideas are very welcome.

EDIT:
I'll summarize here the comments below. onboard, caribou and florence are not installed in my system as shown by the dpkg -L command. I did not install any virtual keyboard manually (for example as gnome-extension). Only for this purpose and as a workaround I tried installing caribou and enabling again the BlockCaribou extension in the hope that it would block the new installed keyboard. It didn't work. I removed completely caribou. Any other ideas?