I was messing around with some programs. Not sure what happened but there was now a watermark saying to activate windows. Said go to settings which I did. Then clicked trouble shoot. Then it went away and said windows is now activated.
Definitely run a full virus scan (Windows Defender will do), but it is likely that you just need to update your system. Something is triggering Windows to think it is not activated, so it complains by showing you the watermark.
This is common enough that Google has a lot of hits about it.