Copy and Paste

About six months ago, I was able to copy and paste from my computer to Microsoft Files--I was able to open up the file that I wanted to copy and paste into the chat column, but recently I have not been able to copy and paste.  

Can you please help me resolve this problem?   I need this matter resolved asap.  

I noticed posted in 2017, a problem, but it doesn't mention if the matter was ever resolved.