editable-grid | Bootstrap grid with CRUD functionality | Grid library

I want to be able to change the value of a TV for Resources shown in a Collections grid using a dropdown select bo.

Can anyone provide an example of how to create a select box in a Collection grid that is either

• populated from the options in an existing Template Variable
• populated from a fixed list, simply options 1, 2, 3

I understand this is possible but can't find an example close enough to what I need to achieve that I can figure it out on my own.

Things I’ve tried are

I have seen Susan Otwell’s example of how to change Created By with a select box http://modxcookbook.com/add-ons/collections/editable-grid-view.html

Discussion linked below addresses a similar problem but remains unanswered https://forums.modx.com/thread/95984/adding-modx-combo-to-collections-list

MIGX configuration and syntax appear similar but not close enough that I can figure what I need to do https://forums.modx.com/thread/91403/single-select-listbox-entries-in-migx

MODx.combo.ComboBox docs look like they have some relevant detail but I don’t know enough to understand if this is useful https://docs.modx.com/revolution/2.x/developing-in-modx/advanced-development/custom-manager-pages/modext/modx.combo.combobox

I've looked for examples of similar dropdowns in the source code of other Extras. I see xtype references but am unable to reverse engineer them to figure what I need to create my own dropdown in the Collections grid.

Susan Otwell's example above creates a dropdown based on xtype modx-combo-user. This looks close to what I need but I can't figure how to adapt this to create a dropdown from either TV values or a fixed list.