Add a checkbox as a custom column
To add a checkbox, you need to enter it in hex or decimal html format
Example: ⬜
&# = decimal format prefix
&#x = hex format prefix
The character might not be supported by the current font so you'll need to upload the Symbola Font.
Once the font is uploaded, can you can display the checkbox using the code below or similar
<span style="font-family: Symbola;">⬜</span>
More information about the unicode font can be found in Unicode Font excerpt.