Can't overthink my daunting, challenging ask

Question

RILFYSXHTWBNLFUFTWNQAFHFTMTWNQYSRTTWBNLFUFTWYSFEUFTWBNLFHFBNTWXHYSHTAFSDTWUFFEKQYSSDUFTWBNLFUFTWFEHFBFUFTWYSNQTWHFTWFEUFHFRTYCQFTWFEYSFETWRIBNHFBNUFTWYSFETWRTHFSDSHYS

Groups of two

Answer 1

Here is my attempt at the answer, which is an image:

Reasoning:

Note the frequent occurance of "TW" after sets of even-numbered letter counts, suggesting a substitution cipher of length 2. (Or just read the hint)
Running this through a Substution Cipher Reducer of length 2 and changing the E's to spaces gives: ABCD FBG HIJK HCL FBG CMG FBJF DCNIO GMPCOG FBG MJQG CH J MGJLRS MCM AFJFG CM LJOTC

Solving this cryptogram gives:
RILFYSXHTWBNLFUFTWNQAFHFTMTWNQYSRTTWBNLFUFTWYSFEUFTWBNLFHFBNTWXHYSHTAFSDTWUFFEKQYSSDUFTWBNLFUFTWFEHFBFUFTWYSNQTWHFTWFEUFHFRTYCQFTWFEYSFETWRIBNHFBNUFTWYSFETWRTHFSDSHYS
S H O W T H E F L A G F O R T H E O N E T H A T W O U L D E N C O D E T H E N A M E O F A N E A R B Y N O N S T A T E O N R A D I O
SHOW THE FLAG FOR THE ONE THAT WOULD ENCODE THE NAME OF A NEARBY NON-STATE ON RADIO

Next we create the key from what we know:

A HF
C KQ
D SD
E UF
F NQ
G TM
H LF
I SH
L AF
M BF
N FE
O YS
R RT
S RI
T BN
U HT
W XH
Y QF
_ TW

Now at this point we have already noticed that the title

is an acronym for CO MD CA, some U.S. states, in alignment with the message referencing a 'state'.

The next step is to stare at this key for an hour trying to make sense of it.

Eventually I started trying rot-n shifts on it, assuming the key had to stand for something meaningful.

Finally, I hit on

rot 21, which lines up with the title theme so far. Here's a rot-21 version of the key data:
A CA
C FL
D NY
E PA
F IL
G OH
H GA
I NC
L VA
M WA
N AZ
O TN
R MO
S MD
T WI
U CO
W SC
Y LA
_ OR

The next step is to try to fill in the gaps, as at this point nothing in the data suggests a "non-state on radio".
We notice #1 and #3, CA and NY, are very populous states. Comparing to a list of US states by population, everything lines up and we can fill the gaps:
A CA
B TX
C FL
D NY
E PA
F IL
G OH
H GA
I NC
J MI
K NJ
L VA
M WA
N AZ
O TN
P MA
Q IN
R MO
S MD
T WI
U CO
V MN
W SC
X AL
Y LA
Z KY
_ OR
At this point we notice an easter egg - the title, CO MD CA decodes to ASU, which is USA backwards.

Now we have a full key if we rotate everything back:

A HF
B YC
C KQ
D SD
E UF
F NQ
G TM
H LF
I SH
J RN
K SO
L AF
M BF
N FE
O YS
P RF
Q NS
R RT
S RI
T BN
U HT
V RS
W XH
X FQ
Y QF
Z PD
_ TW

Going back to the message, we need

THE FLAG FOR THE ONE (US state) THAT WOULD ENCODE THE NAME OF A NEARBY NON-STATE ON RADIO
The most logical nearby non-state is Puerto Rico, or PR. "On radio" implies either morse code or Nato phonetic alphabet, but I had no luck getting either to clue Puerto Rico using the data, or checking all state flags.
Perhaps that is the correct route... but I am proposing a different idea:
If 'on radio' refers to Nato alphabet codes, "Quebec" is nearby to the US, it is not a state (it's not part of the US), and it IS "on radio"... "Quebec" is the Nato phonetic code for "Q".
Even though 'non state' is an odd way to clue a Canadian province, the title DOES say to not overthink this. "nearby non state on radio = Quebec" is certainly simpler than the steps I was taking to try to get Puerto Rico as an answer.
So, what US State would encode 'Q'? Looking at our key, the answer is INDIANA (IN).
We are asked to show the flag, so the final answer is: