As is, it cant be done with the Chrome browser. But 4 methods so it can:
Change that part of the URL from m.facebook to mbasic.facebook
Block the JavaScript function in Chrome via Setting
Apparently this method will work on other non Facebook websites that otherwise block copying of text
When using Chrome,from the three dot menu select Desktop Site.
Change from the Google Chrome browser to the Mozilla Firefox browser. It allows copying by default.
I thought it did when I first tested it,but now it doesent. What's I just imagining it or has something changed?