Hope you are doing well and sorry to hear that. As decscribed, you are unable to fill any data though the fill & sign option opens but no entry is recorded when you write data.
Would you mind sharing the version of the Adobe Acrobat Reader DC you are using? To check the version go to help > About Acrobat and make sure you have the recent version 21.07.20099 installed. Go to Help > Check for updates and reboot the computer.
Also try to repair the installation from help menu (Windows Only) and reboot the computer once.
Make sure the fill color is not set to white as shown below: