This was working until today, and I don’t remember changing anything. I am using a Mac and was first using 5.4.2, removed that and installed 6.01 and still have the problem. I can create a hyperlink without problem using normal create hyperlink actions. If I copy a link from Safari or Firefox, paste it into a writer document and hit return, the text e.g., https://ask.libreoffice.org/new-topic?category=english is on a line but it is not a hyperlink. I can in turn copy that line and paste into a new tab in a browser and open the url.
When you paste something from another application, it is considered as raw text and LO Writer does nothing on it.
Instead of pasting directly your URL, first Insert>Hyperlink at the location where you want it to appear and paste the URL into the URL box.
If direct pasting used to work, check settings in Tools>AutoCorrect>AutoCorrect Options, tab Options. There are 2 checkboxes to enable URL detection: one while typing, the other one while modifying.
If this answer helped you, please accept it by clicking the check mark 
to the left and, karma permitting, upvote it. If this resolves your problem, close the question, that will help other people with the same question.
On a Mac it’s in the Preferences menu instead of Tools.
They both were checked. Tried paste in a new blank document and hit return – still no hyperlink. Unchecked and then checked both boxes and then clicked Apply. Hyperlinks now work. I am not sure why it wasn’t working before this uncheck/check/apply step, but happy that it is now working.