On September 27, 2021, the IRS released the Publication 1220, Specifications for Electronic Filing of Forms 1097, 1098, 1099, 3921, 3922, 5498, and W-2G For Tax Year 2021. There are a number of updates to Pub. 1220 this year, some of which include, but are not limited to:
The new online Information Returns Application for Transmitter Control Code (TCC) and Secure Access
Form 1099-MISC and and Form NEC, particularly due dates and that Form 1099-NEC is part of the Combined Federal/State Filing (CF/SF) Program
Common formatting issues
Format specifications and record layouts
Have a look at the 2021 Pub. 1220 here:
Be ready for your 2021 electronic filing tax year!