Is this actually b/c with the existing library?

I think it is the same library.
We can ask author. Will do.

algo26-matthias/idna-convert#14

I ran composer update. The former one is deleted while the new one is installed.

The version of the library is the same (1.1.0)

use Mso\IdnaConvert\IdnaConvert; is used in /libraries/src/String/PunycodeHelper.php
but we also have
"name": "mso/idna-convert",
in
/libraries/vendor/algo26-matthias/idna-convert/composer.json

Also the namespace in the new library is kept
namespace Mso\IdnaConvert;

autoload does a redirect.
READme.md may have to be modified.

Just a test... remaining is for specialists ?

I confirm though that it works fine. Tested with mail and domain names.

Thanks!

#24009 (comment)

it's because:

1. github redirects old repo to new repo
2. the new repo is just renamed, so it points to exact same git tag
3. the immutable git tag still contains the same code

tks, @glensc

Please read
algo26-matthias/idna-convert#14 (comment)

Tag has changed

I.e.
"algo26-matthias/idna-convert" : "2.*"

Using this last one I also get changes in composer.lock

Tested new version. I get
Class 'Mso\IdnaConvert\IdnaConvert' not found

version 2.0.2 modified the namespace which is now
namespace Algo26\IdnaConvert;
This implies some changes in our code.

#24037 This updates things to latest versions - but yes we should also update to the version 2.0 so there are definitely no conflicts