I'm not sure exactly what "post" means. The brokerage will send you a Form 1099-R for the withdrawal. Are they going to send it for 2023 or for 2024? If they send the 1099-R for 2023 then you were not late, and you don't have a problem. You just report the 1099-R on your 2023 tax return.
If they are going to send the 1099-R for 2024, then yes, you blew the date. But you are almost certain to get a waiver of the penalty. File Form 5329 with your 2023 tax return. Do not file it separately. You will have to take your 2024 RMD before the end of the year. The 1099-R that you get for 2024 will include both the late 2023 RMD and the 2024 RMD. You will report it all on your 2024 tax return.
