I'm also on a Mac (mine is old, mid 2011) and Java, same thing. I didn't have that on 1.14.2, only on 1.14.3. It's not easy to capture a screenshot as it moves like interference. It's impossible to see it in a screenshot as it moves around, it's not static. I tried to make a video on it but all you can see seems lag, so I guess mac users will stuck with this...
I'm also on a Mac (mine is old, mid 2011) and Java, same thing. I didn't have that on 1.14.2, only on 1.14.3. It's not easy to capture a screenshot as it moves like interference. It's impossible to see it in a screenshot as it moves around, it's not static. I tried to make a video on it but all you can see seems lag, so I guess mac users will stuck with this...