You might want to try creating a file called index.theme in .local/share/icons/default/ and putting this in it:
[Icon Theme]
Name=Default
Comment=Default Cursor Theme
Inherits=your-theme-here
cursors can be a pain in the ass to actually make them show up everywhere properly. If you're using Xorg you might also need to set it in .Xresources:
Xcursor.theme: your-theme-here
Xcursor.size: 24
and then if you get into flatpaks you might have to mess with settings in flatseal to give it access to the cursor theme.