Thank you for your comment. I'm not sure for your specific case, but generally the performance largely depends on the terminal emulators in my experience. For example, xterm and Windows ConPTY are super slow which are sometimes 100 times slower than the fastest terminals. urxvt (rxvt-unicode), alacritty, terminology are usually fast. xfce4-terminal, qterminal, mintty are acceptable. VTE based terminals (GNOME terminal, lxterminal, etc.), termit, etc. are slow in my environments.
Actually one of the reason why I wrote this program is to test the terminal performances. When I'm searching the benchmark data of Alacritty, I found this issue https://github.com/alacritty/alacritty/issues/289#issue-2001... where the existing Matrix rain program "cmatrix" is mentioned. I tried "cmatrix" in my terminal (I'm using a terminal which I wrote from scratch for myself) and found that the Matrix rain of "cmatrix" is cheaper than I expected. That is the reason why I wrote "cxxmatrix", a version with additional optical effects written in C++.
The default WSL terminal is slow. I always install an X server. VcXsrv works great, with good Windows clipboard support. Then you can use urxvt or some other Linux terminal that's faster.
I use VcXsrv in the multiwindow mode where it uses the Windows 10 window manager for each X app, instead of being fullscreen. Is that also slow on a 4k screen?