I'm no expert (I can count on one hand the number of these I've filed) but I thought the 3115 had to be filed with a timely filed return?  Maybe @TaxGuyBill knows.

From the instructions page 2:

Attach the original Form 3115 to the filer's timely filed
(including extensions) federal income tax return for the year of
change.

But maybe this will help?:

Late Application
In general, a filer that fails to timely file a Form 3115 will not be
granted an extension of time to file except in unusual and
compelling circumstances. See section 6.03(4)(b) of Rev. Proc.
2015-13 and Regulations section 301.9100-3 for the standards
that must be met. For information on the period of limitations,
see section 5.03(2) of Rev. Proc. 2023-1.