Hello,
thank you anyway for analyzing the problem.
Although I don't agree with the solution.
The registry has been completely cleaned (see the result after installation).
The wapt package has been completely removed and reinstalled.
Not entirely convinced by the answer, I'm continuing my research...

Hello,
I opened a PDF document. I went to
the "Protect / Place Signature" menu.
Once the signature rectangle was placed, nothing appeared in the ID list (see attached copy).

Thank you for your help.
Have a good day.

Hello,
I did download version 41.
I performed a complete uninstall from Windows
and then reinstalled WAPT.
The problem persists.
The certificate is visible under "Sign and certify" as a "Digital ID,"

but it doesn't appear in the "Place a signature" field.
The list of IDs remains...

Hello,
it seems that the Wapt version 12 package available on the Tranquil-It store does not allow the use of certificate IDs for signing documents.

Since the software is installed as administrator, the list of available certificates is not updating.

Can you confirm this?