Hi Chauncey
Hope you are doing well and sorry for the trouble. As described, the fill and sign text is white and you are unable to change it.
I have tried to reproduce the issue on my end and getting the option to change the font color in Fill and Sign Tool as shown below

As you have the latest version of the application, please try to reboot the computer once and see if that helps.
Also try to repair the installation (Win Only) from the help menu. Go to Help > Repair Installation.
If it still doesn't work, please try to reset the Acrobat Preferences to default as described in the help page - https://community.adobe.com/t5/acrobat/how-to-reset-acrobat-preference-settings-to-default/td-p/4792082
You may also try to create a new test user profile with full admin rights or enable the root account in Mac and try using the application there and check .
Let us know if you are referring to something else.
Regards
Amal