Xubuntu 20.04 unable to change cursor size

Solution 1:

Disclaimer: I am under gnome, so some of the items below are best guesses.
Some others also described occasional weird behavior. So I will: 1) Give possible solutions. 2) Ask you to post some info. 3) Give sources.

Possible Solutions

Perhaps you already applied some of these.

1. Reboot (trivial)

2. Execute (you may need xorg-xrdb as per the not-so-old reference; in my system dpkg -S /usr/bin/xrdb returns x11-xserver-utils: /usr/bin/xrdb)

   $ xrdb ~/.Xresources
   

   to load the configuration.

3. Add xrdb ~/.Xresources to ~/.xinitrc or .xprofile.

4. Use xconf-query ("In most cases, any modifications will immediately be propagated to respective applications.")

   $ xfconf-query --channel xsettings --property /Gtk/CursorThemeSize --set <cursor_theme_size>
   

5. Set/modify in ~/.Xresources also Xcursor.theme: <cursor-theme> to see if has any effect. Combine with setting Xcursor.size. Cursor size may respond differently with other cursor themes. I am not sure this is exactly the same as in Settings -> Mouse and Touchpad -> Theme -> Cursor size. Perhaps one is equivalent to the other, plus xrdb ... to load the configuration...

6. Set environment variable XCURSOR_SIZE for a specific application.

7. Try changing the cursor size with the default Window Manager.

Requested extra info

1. Post the output of

   $ xrdb -query
   

2. Which cursor theme are you using (not all support changing the cursor size)? Which is the size you are having, and what you want to have?

Sources

1. https://forum.xfce.org/viewtopic.php?id=12578
2. https://forums.linuxmint.com/viewtopic.php?t=307516
3. https://wiki.archlinux.org/title/Cursor_themes
4. https://archived.forum.manjaro.org/t/cannot-change-mouse-cursor-size-in-xfce/62573/5
5. https://www.funtoo.org/Package:Xfce4-settings