To hide an item from Simple List, you can follow these.
#1. First, find Simple List ID
In my example, it is: section[data-section-id=”66fab517733864572d0d7868″]

#2. Use CSS code like this to Website Tools > Custom CSS
section[data-section-id="66fab517733864572d0d7868"] li:nth-child(2) {
display: none;
}
code will hide item 2 from List Grid

#3. If you want to apply this for desktop only, use this new CSS code
@media screen and (min-width:768px) {
section[data-section-id="66fab517733864572d0d7868"] li:nth-child(2) {
display: none;
}
}
#4. If you want to apply this for mobile only, use this CSS code
@media screen and (max-width:767px) {
section[data-section-id="66fab517733864572d0d7868"] li:nth-child(2) {
display: none;
}
}