[Excel] Conversion Chiffre => Lettre Colonne

Thank you for your help, but for my application to work without waiting time for the user, I need to avoid using VBA code.

I have slightly modified my mockup and I have now found a way to display in a cell the data range I want to use in my EQUIV in the formula:
=Indirect(Address(Match( ...;AB:AB;)))

Here’s what I did to test:
in A1 I write = AB:AB
in A2 I write =Indirect(A1) and I get a #Ref
in A3 I write =Indirect("A1") and I get AB:AB (so the result I want to use)

Previously, I used AB:AB in my formula. Now that the range AB:AB is variable, I can no longer write it "hard-coded" in the formula. So I insert another Indirect in the formula instead of my data range.
=Indirect(Address(Match( ...;Indirect("A1");)))
And there, it's a disaster; I receive a friendly NA error (#N/A)

When I perform a step-by-step analysis of the error, I realize that it translates my Indirect("A1") to $A$19.

How can I resolve this new issue?

P.S.: If you think I should create a new topic for this new problem, don’t hesitate to let me know.

So why post this message in the programming forum?

This is the first time I've read this:
for my application to work without waiting time for the user, I need to avoid using VBA code.

Especially since your reasoning about your formulas is particularly flawed...

I'll leave you, you've already made me waste time trying to help you.

I could indeed have posted in the office section, but needing to use formulas, I preferred to come here and specify [Excel] in the statement (and not VBA).
Maybe my reasoning is wrong, but in any case, I have the merit of having one.
If you couldn't read [Excel] and feel like you've wasted your time, you have no one to blame but yourself for even clicking on the link to this topic.
Thank you in advance for not responding to users if it's to speak in this manner.

Thank you very much Michel for the macro solution, it was helpful to me.