Sorry for the misunderstanding. This is pretty basic: just adding <a href...> </a> tags around any word starting with "https://" in the conversation window, when a user writes/pastes a URL, so that any URL is clickable.
Also, we note that it's not possible to add an underline/comment to a text selection that includes a URL. For example, @VictoriaDemierbe sent this message:
I selected the text 'book our ... lost messages' to add a comment, but because this selection included the URL 'cal.com', I couldn't add the comment. I had to select different text to do so.
But I don't think it matters if it's impossible to underline/comment a text including a URL: the feedback shouldn't be about URLs ;-) and the underlining should be as focused/local as possible, so mostly on short sequences of words, rarely on full sentences.
The case that immediately jumps to my mind is when someone forgets a space between sentences, which might result in a non-link being created (e.g. 'J'aime la musique.Tu aimes la musique aussi?', and then it interprets 'musique.Tu' as a URL). So then the tutor wouldn't be able to comment on it or underline it to show that there's a missing space. (Unfortunately it's not as rare an occurrence as it might seem; I get emails from students all the time which lack spaces between sentences...)
target="_blank" is now fixed on main, but the image fail to build today because UCLouvain seems to have forget to update their own TLS certificates. (I will open a ticket if the error isn't fixed in the next days).
Underlining URLs may be interesting, but for now it's technically not possible due to how the underlining work, and especially to prevent to underline multiple time the same thing. I would describe this issue as "Nice to have".