How do I stop mold from growing on my ceiling after a repaired leak?

Can you run a dehumidifier in this space? Use a hair dryer on low heat to dry out the stained area.

Vinegar!

https://restorationmasterfinder.com/restoration/what-kills-mold-bleach-vs-vinegar/

https://www.servicemaster-restoration-cleaning.com/2017/03/30/mold-myths/

https://www.servicemasterrestore.com/blog/mold-damage/mold-myths-will-vinegar-kill-mold/

Eventually I would cut a hole in the drywall and see if the mold is in the wall or ceiling. If so, remove drywall, remediate and replace the drywall. Mold, if left unattended can cause serious damage which is expensive to remediate and unhealthy to boot.

You will need to remove the damaged drywall and any insulation. The mold spores will spread and more damage will occur.

I Agree. Fix now to prevent further problems. Are you sure the roof leak is fixed?

Spray it with bleach.

Ok-I got a dehumidifier, I sprayed it with vinegar and now I'm watching for a break in the storms to have a new roof, insulation put on and in. And I'm contemplating mold remediation. Before, during or after the new roof?

The mold remediation will be done from the inside unless you are re-sheathing that part of the roof due to rot. If it turns out you have mold growth on the underside of the roof sheathing, a remediation company will spray an encapsulating fungicide to inhibit further growth. The same company may or may not also do any insulation and sheetrock repair, although you could do that to save some money. So, the timing in relation to the roof repair is not important. Have someone come take a look at it now and have the work done as long as there are no active leaks.