Here is a script that is easier for "grandma" to use:
zoom - Script to set Nautilus Thumbnail size
# NAME: zoom
# DESC: Change nautilus thumbnail size based on parameter 1
# For Ask Ubuntu question: https://askubuntu.com/questions/1097934
# DATE: December 7, 2018
if [[ $# -ne 1 ]]; then
echo "Usage: 'zoom 999'"
echo "Where 999 is zoom factor, eg 400 = 400% zoom"
gsettings set org.gnome.nautilus.icon-view thumbnail-size "$1"
Installation and Usage
Place the file
zoom in your search path.
Mark the file executable with
chmod a+x /search-path-name/zoom
Call the script from terminal using
zoom 999 where 999 is the zoom factor. For example
zoom 400 will have
nautilus zoom by 400%.
The script can be enhanced to use
zenity for a desktop shortcut with GUI pop up window that prompts for zoom percentage.