Cannot write the character "_" on the French BÉPO keyboard layout

Distribution

Linux Mint wilma 22 x86_64

Package version

Cinnamon 6.2.9

Graphics hardware in use

Intel UHD Graphics 620

Frequency

Always

Bug description

On the standard BÉPO keyboard layout available on Linux Mint, available by default under the name "French (BEPO)" on the Keyboard application, it's currently impossible to write the character "_", which is normally accessible using the combination AltGr + Space.

I also found a thread there reporting the same issue : https://forums.linuxmint.com/viewtopic.php?t=369511, but no bug report has been made on this issue.

Here's, what it should be like, according to the official bepo.fr website:

And here's what we have currently in the Keyboard application:

Steps to reproduce

Press the combination [AltGr] + [Space] in a text field.

Expected behavior

Expected behaviour: prints the character "_".
Current behaviour: prints a regular space " ".

Additional information

No response

Start by reproducing the issue in the Cinnamon Keyboard application on Linux Mint with the standard French BÉPO layout, using AltGr + Space in a text field. Compare the configured layout with the official bepo.fr reference and the attached screenshots; done means the combination produces "_" rather than a space.