I look at the log in the configuration log item. If I try to copy by clicking on the clipboard icon that appears when hovering over each error line, the right side will be blank. It has not been copied. If I reload, the error list will be displayed again.
I can click the lower triangle to view or select the details of the error. However, I can not copy. When I try to copy, the details are closed.
This has been confirmed since the NC15 era, but I hope to solve it soon.
Unfortunately your report misses some essential information, like which web browser you’ve tried, which client OS you are using, to which application you want to transfer the data and which Nextcloud version you’ve tested.
I just tested it with Firefox 68.0.1 and Nextcloud 16.0.3 and it works as expected. I’ve opened the system log panel, selected a record, clicked on the clipboard icon, selected “copy formatted” or “copy in raw format”, opened e.g. Windows Notepad and pasted the content to it.