Categorical Multi select option is not shown in the drop down menu

Drop-Down Menu or list box for multiple selection

Filter Data from Your Views - Tableau

Dropdowns: Design Guidelines

Control drop-down list appearance and behavior - MATLAB

The Dropdown Column – Support

Filter Data from Your Views - Tableau

Creating 3 level (multilevel) drop down in angular - Stack Overflow

Use the dropdown (multi-select) block - Tripetto Help Center

Filter Data from Your Views - Tableau

Custom Single/Multi Select In Pure JavaScript - vanillaSelectBox

Control drop-down list appearance and behavior - MATLAB

Dropdown Menu Element – Surveys