No transparent backround with xcompmgr compositor

[CocolinoFan]

Describe the bug
Background not transparent.

To Reproduce
Install dwm (emerge --ask x11-wm/dwm)
Install cmatrix (emerge --ask app-misc/cmatrix)
Install xcompmgr (emerge --ask x11-misc/xcompmgr)

Expected behavior
Expected transparent background as in Gentoo the package gets build from source.

Screenshots

• Gentoo Linux | Kernel: 6.7.4-gentoo-dist
• cmatrix 2.0-r4

[CocolinoFan]

[UPDATE]
Changing the compositor to picom did not seam to make a difference.
But using the -i option of picom makes the cmatrix's background more transparent as you would expect.