My bad. I forgot that some logic was added to linkify as well so as to minimise the false positives. I am not a dev but I was involved in the discussion about this.
Just type https://medium.com rather than medium.com and the link should work. I believe that the protocol identifier now triggers the linking so that there are no false positives for text that is not actually a URI. This was especially true for the filenames of python and perl scripts such as file.py and file.pl.
Personally I feel that Joplin turning anything that looks like a hyperlink into a hyperlink would be a retrograde step. Then again, it would not affect me as I have linkify switched off and use standard Markdown to create hyperlinks only when I need them.