Welcome to the community, @Mope_Akande! :grinning_face_with_big_eyes: This is doable using an automation. For the automation trigger, set it to “When record is updated”, looking specifically for changes to the formula field that creates the checkbox list. Here’s a shortcut way to build the markdown without having to manually type it all out for both options:
IF(
Option,
"[ ] " & SUBSTITUTE(
SWITCH(
Option,
"Option A", "x,y,z",
"Option B", "red,green,blue"
), ",", "\n[ ] "
)
)
The only action you’ll need will be “Update record,” which will copy the formula field output into the long text field with rich text enabled. Once this automation is enabled, any change to the formula field’s output will trigger the automation to copy that output to the rich text field, so you can hide the formula field and just use the rich text field.
From your description, it sounds like the formula output will only change once, so you shouldn’t have to worry about your rich text checklist being erased.