unclutter will do this automatically, but there is an easy way to do it manually with xsetroot -cursor

Hiding ∞

# TODO - random name
emptycursor_filename='emptycursor-data.bmp'
  
emptycursor_data=$( \cat <<'HEREDOC'
#define nn1_width 16\n#define nn1_height 16\nstatic unsigned char nn1_bits[] = {\n0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,\n0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,\n0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};\n
HEREDOC)
  
\rm  --force  "$emptycursor_filename"
\echo  "$emptycursor_data" > "$emptycursor_filename"
\xsetroot  -cursor "$emptycursor_filename" "$emptycursor_filename"
\rm  --force  "$emptycursor_filename"

Showing ∞

\xsetroot  -cursor_name  left_ptr