Gantt read only column based on a condition

Hello. I would like to make the start date of a task ready only based on whether or not a custom property I have, the actual start date is null or has a value. How do I accomplish this?

Hi Jon,
If I understand you correctly, you want to make task grid cells with a start date, read-only or not, based on some property from your data, am I right?
By default you cannot change data from the grid directly - clicking on the cells will open a lightbox, from where you can change the data, as in the following screenshot: https://prnt.sc/pdrzfn
If you meant this case, I left an example of disabling time selectors in the fragment below.
To directly modify data from a grid, you must use built-in or custom editors (https://docs.dhtmlx.com/gantt/desktop__inline_editing.html).
You can see how it looks in the following screenshot: https://prnt.sc/pds10v
If you meant this editing, I left an example of disabling certain cells based on the custom property dateEditable , using onBeforeEditStart
event(https://docs.dhtmlx.com/gantt/desktop__inline_editors_ext.html#events)
Of course, you can use more appropriate events and conditions.
A fragment with examples of disabling lightbox select inputs and grid cells:
https://snippet.dhtmlx.com/b9d935007

Also, if ready only in the post is not a typo, and you want to change the actual start date when a task is loaded - you can look at onTaskLoading event(https://docs.dhtmlx.com/gantt/api__gantt_ontaskloading_event.html).