If he is not in a combat zone or on a continency operation authorized by the Secretary of Defense then his tax return has to be filed on or before October 17, 2022.  There are no second extensions.

However, if he is filing the 2021 tax return for a tax refund then the return can be filed at any time on or before October 15, 2025 without penalty.

....always an additional BUT

IF he does file after 15 October 2022...then he will have to file by mail on paper, no e-filing with TTX after that date  (with whatever processing delays are occurring at that time..) AND he would have to use the desktop/download software on a full MAC or Windows computer since the Online software will be shut down for 2021 tax returns soon after15 October.

In addition to the 6-month extension (automatic 2-month and additional automatic 4-month extensions), he can request a discretionary 2-month additional extension of time to file his return to December 15, 2022, if he is a calendar-year taxpayer.

To request this extension, he must send the IRS a letter explaining the reasons why he needs the additional 2 months. He must send the letter by the extended due date (October 17, 2022, if he is a calendar-year taxpayer) to the following address:

He won’t receive any notification from the IRS unless his request is denied.

https://www.irs.gov/publications/p3