I believe that form went the way of the dinosaurs in 2006?

The only additional "extension" past 10.15.2021 would be due to disaster circumstances and doesn't require filing a form.  The IRS "automatically" knows by the ZIP code on the tax return.  Or, so they & the software says.

You must be remembering when Form 4868 only extended until August and Form 2688 could get an extra two months extension to October 

You’ve come to an Intuit site supporting tax professionals, and you may be looking for support as an individual taxpayer. Please visit the TurboTax Help site for support.

Or maybe remembering even further back. In the 80's the 4868 was good for 2 months to June; then 1st 2688 explained need to get to August and another 2688 with "dog eat my homework" got 2 more months to October.

[Oh the good times!!!]

You mean they changed the due date from March 15?  Thanks for letting me know.  No one told me.  

@BobKamman King Egbert is not amused (at that reply)....