External Monitor Lag when using HDMI adapter

Hi, Apple Community!

I recently got a Mini-Display port to HDMI adapter a while back and have attempted to use it with my Phillips Monitor 278E1A; it worked however forced a retnia resoulution and it caused my computer to lag really badly when i used my external monitor but if it was pluged in and i used my main monitor even if something was open on my external monitor my main one had no lag. It only lags when I have my mouse on the external one. I went into safe mode and put it at its native resoulution 1080p and it was still laggy. I have tried 2 display adapters; multipule monitors and done alot of digging on the internet. I dont know why it does this and need help fixing it so it dosent lag like how it now does. I cant even watch youtube on my external monitor because it will often keep buffering to keep up with the frame rate (which I dont know why it has to).

Someone please help me with this ASAP.

From,

Sam

(PS. I know my name is really cringy but I made it when I was like 12 sooo)