I filed an amended return for 2021, it was accepted by the IRS on December 9,2024 but I have not heard anything else about it. Is there something that I need to do ?

Do not expect quick results from amending. It can take four months or more for the IRS to process an amended return.  

You can watch for information here:

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

It can take the IRS 16 weeks or longer to process and amended tax return.

Go to this IRS website for the status of an amended tax return - https://www.irs.gov/filing/wheres-my-amended-return