For people with the June 15th extended deadline?   

IRS made this info public back a month ago, you cant Efile extensions after the May 17th deadline, even if you have an extended June 15th deadline.

Taxpayers living in Texas, Oklahoma, Louisiana, Alabama, and Kentucky have until June 15, 2021 to file most types of returns that were due after February 11,2021. The IRS says that the only way for those taxpayers to file an extension is on paper or to have filed an extension on the appropriate due date which is probably March 15, 2021, April 15, 2021, or May 17, 2021 depending on which type of return is being filed..