Hi brothers,

I using windows 10, currently have 2 x 1080p monitor at 24".

Now i plan to upgrade 1 of them into 4k. Possible to use split screen mode? Since one is 4k and one is 1080p.

Right now i using 1 for windowed gaming and 1 for watching movie/surfing internet.

I plan to change the main monitor into 4k. After that i wonder if i can still use the secondary one in 1080p?

What is the size of your 4k monitor?
If it is 27" or 28" and you using zoom 150% in windows 10 while the other monitor is normal 100%, then you will regret it.
Your main desktop monitor will be clear and the other monitor will be very blur.
I think it is because windows 10 adjust and zoom again from your main desktop.

4k would be 32", the 1080p is currently 24".
I dont actually use the extend mode.

u are using 2 monitor and normally will use extend mode on 2nd monitor.
then if u din use extend mode, then what mode do u use??
duplicate mode

Main monitor will be 4k at 32", secondary monitor is 1080p at 23". ok ka like this?

You OK with imbalanced setup then it's OK.